Algebra Definition and 999 Threads

Algebra (from Arabic: الجبر‎, romanized: al-jabr, lit. 'reunion of broken parts, bonesetting') is one of the broad areas of mathematics, together with number theory, geometry and analysis. In its most general form, algebra is the study of mathematical symbols and the rules for manipulating these symbols; it is a unifying thread of almost all of mathematics. It includes everything from elementary equation solving to the study of abstractions such as groups, rings, and fields. The more basic parts of algebra are called elementary algebra; the more abstract parts are called abstract algebra or modern algebra. Elementary algebra is generally considered to be essential for any study of mathematics, science, or engineering, as well as such applications as medicine and economics. Abstract algebra is a major area in advanced mathematics, studied primarily by professional mathematicians.
Elementary algebra differs from arithmetic in the use of abstractions, such as using letters to stand for numbers that are either unknown or allowed to take on many values. For example, in



x
+
2
=
5


{\displaystyle x+2=5}
the letter



x


{\displaystyle x}
is an unknown, but applying additive inverses can reveal its value:



x
=
3


{\displaystyle x=3}
. Algebra gives methods for writing formulas and solving equations that are much clearer and easier than the older method of writing everything out in words.
The word algebra is also used in certain specialized ways. A special kind of mathematical object in abstract algebra is called an "algebra", and the word is used, for example, in the phrases linear algebra and algebraic topology.
A mathematician who does research in algebra is called an algebraist.

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  1. bornofflame

    [Linear Algebra] Construct an n x 3 matrix D such that AD=I3

    Homework Statement Suppose that A is a 3 x n matrix whose columns span R3. Explain how to construct an n x 3 matrix D such that AD = I3. "Theorem 4" For a matrix A of size m x n, the following statements are equivalent, that is either all true or all false: a. For each b in Rm, Ax = b has a...
  2. B

    MHB Simple algebra solve (1-x)(1-0.03)^2 = 0.667

    I am following a book and can't arrive at the same answer. Not sure what to try next. (1-x)(1-0.03)^2 the book then says = 0.667 x= 0.291 my attempt (1-x)(1 - .03)(1 - .03) then i get confused (1-x)(0.9409) not sure ><
  3. M

    MHB Algebra Not Needed After High School

    Why do students say, as a typical excuse, "I don't need this algebra stuff because it is not required for success after high school"? What do you say? I say we use algebra everyday and don't even realize it.
  4. L

    How Does the Absorption Law Simplify This Boolean Function?

    Homework Statement i'm viewing an example written in class. it looks like this: f(x1, x2, x3, x4) = [(not x1) * x2 * x4] ∨ [x2 * x3 * x4] what should be function after applying absorption law? Homework Equations i know how another option called "gluing" works: [x1 * x2 * x3] ∨ [(not x1) *...
  5. S

    I What is the definition of a Semi-simple Lie algebra?

    Hello! I am a bit confused by some definitions. We have that a Lie algebra is abelian if ##[a,b]=0## for all ##a,b \in L## and ##L'## is an invariant subalgebra of ##L## if ##[a,b]=0## for all ##a \in L'## and ##b \in L##. From here I understand that ##L'## is abelian. Then they define a...
  6. R

    Creating system of equations from word problem optimization

    I have this word problem, and was wondering how I would go about creating a system of equations. Here is the question: Problem: You are a small forest landowner, and decide you want to sustainably harvest some of timber on your property. There are costs related to the infrastructure needed to...
  7. F

    Linear algebra matrix to compute series

    Post moved by moderator, so missing the homework template. series ##{a_n}## is define by ##a_1=1 ## , ##a_2=5 ## , ##a_3=1 ##, ##a_{n+3}=a_{n+2}+4a_{n+1}-4a_n ## ( ##n \geq 1 ##). $$\begin{pmatrix}a_{n+3} \\ a_{n+2} \\ a_{n+1} \\ \end{pmatrix}=B\begin{pmatrix}a_{n+2} \\ a_{n+1} \\ a_{n} \\...
  8. S

    MHB A problem about submodules in "Advanced Modern Algebra" of Rotman

    Please, can someone help me with this? Let $M$ be a left $R$-module over a ring $R$. Let $J$ be a left ideal in $R$ generated by $r$: $J=Rr=<r>$. Now $JM=\{am \ | \ a \in J \ and \ m \in M\}$ Prove that $JM$ is a submodule of $M$. This is an example in Rotman's book "Advanced Modern Algebra"...
  9. Rin

    Algebra Books Best for Mathematics & Algebra Self-Study with Proofs?

    Hello, I've been trying to improve my algebra since I've never been particularly good with math. I'm going through Serge Lang's Basic Mathematics textbook and while I have been learning a lot his proof-based exercises are a pain to get through and the back of the book only provides answers for...
  10. B

    I Can we construct a Lie algebra from the squares of SU(1,1)

    I am trying to decompose some exponential operators in quantum optics. The interesting thing is that the operators includes operators from Su(1,1) algebra $$ [K_+,K_-]=-2K_z \quad,\quad [K_z,K_\pm]=\pm K_\pm.$$ For example this one: $$ (K_++K_-)^2.$$ But as you can see they are squares of it. I...
  11. L

    Linear Algebra - Find an orthogonal matrix P

    A problem that I have to solve for my Linear Algebra course is the following We are supposed to use Mathematica. What I have done is that I first checked that A is symmetric, i.e. that ##A = A^T##. Which is obvious. Next I computed the eigenvalues for A. The characteristic polynomial is...
  12. A

    A How to simplify the solution of the following linear homogeneous ODE?

    During solution of a PDE I came across following ODE ## \frac{d \bar h}{dt} + \frac{K}{S_s} \alpha^2 \bar h = -\frac{K}{S_s} \alpha H h_b(t) ## I have to solve this ODE which I have done using integrating factor using following steps taking integrating factor I=\exp^{\int \frac{1}{D} \alpha^2...
  13. P

    Linear Algebra, Find a matrix C st CA = B

    Homework Statement Let A be an arbitrary m× n matrix. Find a matrix C such that CA = B for each of the following matrices B. a. B is the matrix that results from multiplying row i of A by a nonzero number c. b. B is the matrix that results from swapping rows i and j of A. c. B is the matrix...
  14. Ty Ellison

    Linear Algebra: Parametric Solution Set

    Homework Statement [/B] Suppose the solution set of some system Ax = b , Where A is a 4x3 matrix, is *Bold characters are vectors* x_1= 1 + 3t x_2 = 2 - t x_3 = 3 + 2t where t is a parameter and can be any number. a) How many pivots are in the row echelon form of A? b) Let u, v, w be the...
  15. M

    (Boolean Algebra) Did I write this logic expression correctly?

    Homework Statement My solution, is this correct? This is what I came up with. Y=A+((A*B)+B+C'+(B+C'*D)+D) Is it safe to say that it is correct or did I make a mistake?
  16. C

    A Is the proof of these results correct?

    Hello, Below are two results with their proof. Of course, there may be several ways to prove these results, but I just need some checking. Can someone check carefully if the math is OK ? (but very carefully, because if there is a failure, I will be murdered :-) ) ? thx. Claim 1: Let ##L/K## be...
  17. Sorcerer

    I What are the differences between matrices and tensors?

    I have not really finished studying linear algebra, I have to admit. The furthest I have gotten to is manipulating matrices a little bit (although I have used this in differential equations to calculate a Wronskian to see if two equations are linear independent, but again, a determinant is...
  18. N

    Laplace expansion of the inner product (Geometric Algebra)

    Homework Statement Prove that ##\vec {a} \cdot (\vec {b} \wedge \vec {C_r}) = \vec {a} \cdot \vec {b} \vec {C_r} - \vec {b} \wedge (\vec {a} \cdot \vec {C_r})##. Note that ##\vec {a}## is a vector, ##\vec {b}## is a vector, and ##\vec {C_r}## is an r-blade with ##r > 0##. Also, the dot...
  19. C

    MHB [Linear Algebra] - Find the shortest distance d between two lines

    Let L1 be the line passing through the point P1=(−2,−11,9) with direction vector d2=[0,2,−2]T, and let L2 be the line passing through the point P2=(−2,−1,11) with direction vector d2=[−1,0,−1]T Find the shortest distance d between these two lines, and find a point Q1 on L1 and a point Q2 on L2...
  20. D

    B Calculating Rod Speeds with Algebraic Formulas

    I am trying to create a formula for a spreadsheet to calculate values and it has been thirty years since high school algebra. Here are the formulas I need to rearrange. w=(d/r)/t v=d/t w is an unknown constant and I have values for v1 and r1 I need the formula to spit out v2 if I input r2 in...
  21. N

    Understanding Linear Algebra Subspaces and Matrices: A Homework Guide

    Homework Statement I have an assignment for my linear algebra class, that I simply cannot figure out. Its going to be hard to follow the template of the forum, as its a rather simply problem. It is as follows: Given the following subspace (F = reals and complex) and the "linear image"...
  22. M

    I If A is an algebra, then its uniform closure is an algebra.

    Let me give some context. Let X be a compact metric space and ##C(X)## be the set of all continuous functions ##X \to \mathbb{R}##, equipped with the uniform norm, i.e. the norm defined by ##\Vert f \Vert = \sup_{x \in X} |f(x)|## Note that this is well defined by compactness. Then, for a...
  23. 4

    I Solving Dirac Algebra Arithmetic

    I have a question regarding the Dirac notation arithmetic. Below is a measurement of a general 2 qubit state with the measurement operator M=|0><0| ⊗ I , where I is the identity operator. To go from equation (2) to equation (3), I've been converting all the Dirac notation to matrices and column...
  24. S

    A Are bounded operators bounded indepedently on the function?

    Hi thanks to George, I found the following criteria for boundedness: \begin{equation} \frac{||Bf(x)||}{||f(x)||} < ||Bf(x)|| \end{equation} If one takes f(x) = x, and consider B = (h/id/dx - g), where g is some constant, then B is bounded in the interval 0-##\pi##. However, given that I...
  25. Shai

    Determine the values of a and b that have inflection points

    <Moderator's note: Moved from a technical forum and thus no template.> The title isn't complete this is what I meant to say: Determine the values of aa and bb where the function has inflection points (x2+ax+b)(ex) I made the second derivative $$f''(x) = 2 e^x + 2 a e^x + b e^x + 4 e^x x + a...
  26. A

    Heisenberg algebra Isomorphic to Galilean algebra

    Homework Statement Given for one-dimensional Galilean symmetry the generators ##K, P,## and ##H##, with the following commutation relations: $$[K, H] = iP$$ $$[H,P] = 0$$ $$[P,K] = 0$$ Homework Equations Show that the Lie algebra for the generators ##K, P,## and ##H## is isomorphic to the...
  27. C

    B Calculating the area of a circle or square using decimals

    I came across something that is completely counter-intuitive, and I'm wondering if I'm correct or not. If a square has a side that is .8m someone would do .8 time .8 which is .64. How can an area be smaller than a side I thought and so I looked it up and found only one site that said something...
  28. M

    Best Algebra TextBook For Self Learner?

    Hi there, I have been searching multiple websites and forums but have not found a cohesive answer to my queries. I am currently going through this textbook to learn pre-algebra: https://www.amazon.com/dp/0618250034/?tag=pfamazon01-20 Also, is this a good book to be studying as an autodidact...
  29. D

    B Why Does This Algebraic Identity Work in Relativistic Doppler Calculations?

    I seem to remember this Algebra identity being covered in one of my classes years ago, but it has cropped back up in studying the relativistic doppler effect for light. Can anyone please show me the intermediate steps to show that: (1+x)/(sqrt(1-x^2) = sqrt((1+x)/(1-x)) or similarly...
  30. mr.tea

    I Help Needed: Understanding Hungerford's Algebra Book Proofs

    I am trying to learn about free groups(as part of my Bachelor's thesis), and was assigned with Hungerford's Algebra book. Unfortunately, the book uses some aspects from category theory(which I have not learned). If someone has an access to the book and can help me, I would be grateful. First...
  31. Y

    Linear Algebra - Incidence Matrix of an RLC Ckt

    <Moved from a homework forum. Template removed.> I can't find any documentation on how to do this. I remember in linear algebra how to find the incidence matrix of an electrical network of purely resistors. Put how do I find it of a RLC circuit with resistors, inductors, and capacitors? I can't...
  32. M

    Linear Algebra: Verifying A^2-2A+7I=0

    Homework Statement Verify that A^2-2A+7I=0Homework Equations A is a squared matrix and I is the identity matrix. The Attempt at a Solution I squared a matrix, which I called A, by multiplying the two A matrices together, then I subtracting the new matrix with the third matrix 2A, then I added...
  33. Philosophaie

    I Exterior Algebra: (A1−A2,B1−B2,C1−C2) ∧ (A1,B1,C1) Explained

    (A1−A2,B1−B2,C1−C2)∧(A1,B1,C1)(A1−A2,B1−B2,C1−C2)∧(A1,B1,C1) ##=((A1−A2)∗B1−(B1−B2)∗A1)∗(\hat x \wedge \hat y)+((C1−C2)∗A1−(A1−A2)∗C1)∗(\hat z \wedge \hat x)+((B1−B2)∗C1−(C1−C2)∗B1)∗(\hat y \wedge \hat z)## Is this the correct exterior product?
  34. J

    A Newton's Generalized Binomial Theorem

    I'm trying to expand the following using Newton's Generalized Binomial Theorem. $$[f_1(x)+f_2(x)]^\delta = (f_1(x))^\delta + \delta (f_1(x))^{\delta-1}f_2(x) + \frac{\delta(\delta-1)}{2!}(f_1(x))^{\delta-2}(f_2(x))^2 + ...$$ where $$0<\delta<<1$$ But the condition for this formula is that...
  35. 1

    Find Y when AxY=B, BxY=C, and B is unknown

    How do I: Find Y when AxY=B, BxY=C, and B is unknown? (A and C are known) Example: If A=100 and C=169 then Y=1.3 and B=130 I assume I use log or pow but cannot figure it out. Thanks.
  36. T

    Algebra Question Solved | Quick and Easy Solution

    Sorry, I posted too soon. I was able to figure it out.
  37. S

    Algebra Recommended books for linear algebra and multi-variable calculus

    hey everyone just started university and the jump i feel is huge from a level and was just wondering if you guys knew of any books that had linear algebra and/or several variable calculus in them but displayed and explained stuff in a clear simple way? or if anyone has any websites that do the...
  38. S

    Hoffman, Kunze Linear Algebra book: which topics to study QM?

    I've started self-studying quantum mechanics. It's clear from google searching and online Q.Mech lectures, I'll need to understand linear algebra first. I'm starting with finite-dimensional linear algebra and Hoffman, Kunze is one of the widely recommended textbooks for that. I need help...
  39. Schaus

    Linear Algebra - REF with another variable

    Homework Statement Determine the values of a for which the following system of linear equations has no solutions, a unique solution, or infinitely many solutions. You can select 'always', 'never', 'a = ', or 'a ≠', then specify a value or comma-separated list of values. x1−2x2+2x3 = −1...
  40. jlmccart03

    Courses Calculus 3 -- looking for ways to help me understand

    So I am in calculus 3 this year and have passed both calc 1 and 2 with a B and C+ respectively. I could have gotten a better grade but was lazy. I was lazy by using calculators and not actually learning the arithmetic and algebra. Now one serious issue I have is Trig. I can never remember trig...
  41. The Bill

    Algebra Resources for tutoring high school algebra

    I may be doing Algebra I tutoring for high school students soon. What are some good resources for exercises and intuitive/novel explanations for topics some students find sticky, etc.? One resource I'm sure I'll be using is the Schaum's Outline of Elementary Algebra, 3ed. What I'd also like is...
  42. D

    Courses Linear Algebra or Computer Science?

    I am going to have two slots available this year for electives and I want to use one of them for Astronomy. For the other, I am struggling to decide between Linear Algebra or Computer Science (CIS 210 at my university) which focuses on Python programming. If I can only choose one, which is more...
  43. P

    Show this integral defines a scalar product.

    Hi, I'm stuck on a problem from my quantum homework. I have to show <p1|p2> = ∫(from -1 to 1) dx (p1*)(p2) is a scalar product (p1 and p2 are single variable complex polynomials). I've figured out how to show that they satisfy linearity and positive definiteness, but I'm completely stuck on...
  44. R

    How Can I Solve This Equation to Find the Correct Expression?

    Homework Statement I am trying to solve for ##P## in the equation: $$Q=\frac{2RP}{\sqrt{\sigma_{T}^{2}+\left(2RPr\right)^{2}}+\sigma_{T}} \tag{1}$$ The correct answer must be: $$\boxed{P=\frac{Q\sigma_{T}}{R(1-r^{2}Q^{2})}} \tag{2}$$ I am unable to get this expression. Homework...
  45. D

    B Looking for some intuition on a basic Algebra equation

    This isn't for math homework. I'm in self study and came across something in my book that I'm seeking clarification for. The equation: $$0.3\left(50-x\right)=6$$ The solution: $$3\left(50-x\right)=60$$ $$150-3x=60$$ $$-3x=-90$$ $$x=30$$ Simple enough. My question is in regards to this: The...
  46. A

    Schools Possible to skip College Algebra?

    I heard College Algebra is just a review of Algebra 2 but goes in depth more. I was wondering if it's possible to skip College Algebra if a person has an A in Alg 1 and Alg 2?
  47. S

    I Lie Algebra states of a representation

    Hello! I am reading some representation theory/Lie algebra stuff and at a point the author says "the states of the adjoint representation correspond to generators". I am not sure I understand this. I thought that the states of a representation are the vectors in the vector space on which the...
  48. P

    Algebra What is a great book for completing Algebra and trigonometry?

    Once I complete high school geometry, I am planning to take algebra 2 and trigonometry next. I am asking if there are good textbooks out there that provide a full course of algebra 2 and trigonometry. Or should I take these two courses separately? By the way, I am self-studying.
  49. R

    Courses Is proof based Linear Algebra be similar to Abstract Algebra

    I know both are different courses, but what I mean is, will a proof based Linear Algebra course be similar to an Abstract Algebra course in terms of difficulty and proofs, or are the proofs similar? Someone told me that there isn't that much difference between the proofs in Linear or Abstract...
  50. Mr Davis 97

    Proving det(A) > 0 for A^3 = A + 1 over R using linear algebra

    Homework Statement If A is an n x n matrix over R such that A^3 = A + 1, prove that det(A) > 0 . Homework EquationsThe Attempt at a Solution So, what I've done is factor the expression to get A(A+1)(A-1) = 1, then taking the determinant of both sides, I get det(A)det(A+1)det(A-1) = 1. I...
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