Product rule Definition and 139 Threads

In calculus, the product rule (or Leibniz rule or Leibniz product rule) is a formula used to find the derivatives of products of two or more functions. For two functions, it may be stated in Lagrange's notation as




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{\displaystyle (u\cdot v)'=u'\cdot v+u\cdot v'}
or in Leibniz's notation as







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{\displaystyle {\dfrac {d}{dx}}(u\cdot v)={\dfrac {du}{dx}}\cdot v+u\cdot {\dfrac {dv}{dx}}.}
The rule may be extended or generalized to products of three or more functions, to a rule for higher-order derivatives of a product, and to other contexts.

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  1. T

    Differentiation by the Product Rule

    Hi I have been asked to solve the following 2 questions using 'rules' to find the derivative. (The Product Rule, The Chain Rule or The Quotient Rule.) but I can't remember what these rules are or how they are used Q1: Find the equation of the tangent to each of the following curves at the...
  2. K

    The product rule applied to the equation for work

    This is NOT homework... If one takes the formula for work, which is force times distance, one can get the formula for power by taking the derivative of it with respect to time. But if we really do this correctly (by using calculus), we get: power=distance*(change of force/change in...
  3. F

    Product rule for two derivatives

    Homework Statement I was just wondering if there is a formula for the product rule when you take two derivatives ... ? Homework Equations I know the product rule for one derivative .. is u'v + uv' ! The Attempt at a Solution I just want a formula without a proof
  4. M

    Simplifying derivative after using product rule

    Homework Statement Find the derivative of the function: f(x) = x^2((x-2)^4) Homework Equations f`(x) = (u)(y`) + (u`)(y) The Attempt at a Solution Via the product rule I got [x^2(4(x-2)^3)] + [(2x)(x-2)^4] the book then goes on to give the solution as 2x(x-3)^3 * (3x-2) I'm...
  5. B

    Simple question regarding Product Rule

    Homework Statement As part of a first order differential equation I need to find \frac{d}{dt}(mv) where v=\frac{dy}{dt} Homework Equations Product Rule. The Attempt at a Solution \frac{d}{dt}(m\frac{dy}{dt}) = m*\frac{d}{dt}\frac{dy}{dt} + \frac{dm}{dt}\frac{dy}{dt} = ?? I...
  6. T

    STUPID Vector qusetion - dont understand dot product rule

    Homework Statement The points A and B have position vectors a = (2,2,1) and b (1,1,-4) respectively relative to an origin O. (im using column notation for shorthand) Prove that OA is perpendicular to AB Homework Equations The Attempt at a Solution To be perpendicular the...
  7. Saladsamurai

    Why Does the Curl Product Rule Seem Confusing?

    Curl Product Rule confusion? Homework Statement In Griffith's Introduction to Electrodynamics, he gives the rule: \nabla\times(\bold{A}\times\bold{B})=(\bold{B}\cdot\nabla)\bold{A}-(\bold{A}\cdot\nabla)\bold{B}+\bold{A}(\nabla\cdot\bold{B})-\bold{B}(\nabla\cdot\bold{A}) Now I know I am...
  8. M

    Extended product rule for derivatives

    Can someone please explain it to me? My handwriting wasn't at its best when I was taking notes in class and now I can't read it. The teacher showed an example that I jotted down but what's the general rule?
  9. A

    Exploring y", y" with the Product Rule

    y=-1/2 x cosx y'=1/2 x sinx + cos x -1/2 y"= 1/2 x cosx - sin x 1/2 + cos x + -1/2 - sin x y"= 1/2 x cos^2x I used the product rule (fg)'=fg'+gf'
  10. G

    Product Rule (Thinking/Inquiry)

    Determine a quadratic funtion f(x) = ax^2 + bx + c who graph passes through the point (2,19) and that has a horizontal tangent at (-1,-8). My attempt at this solution is: f(x) = ax^2 + bx + c f'(x) = 2ax + b LOL its not much but i really have absolutely no idea where to go from here :S
  11. F

    Optimizing the Product Rule: Common Error Help for (5x-2)^3 / (2x+5)^4

    y = ( 5 x-2 ) 3 / ( 2 x+5 ) 4 I do it this way: f(x) = (5x-2)3 g(x) = (2x+5)-4 f'(x) = 3(5x-2)2 g'(x) = -4(2x+5)-5 By using the product rule: [3(5x-2)2](2x+5)-4 + (5x-2)3[-4(2x+5)-5] 3(5x-2)2(2x+5)-4 -4(2x+5)-5(5x-2)3 What's wrong with this answer?
  12. C

    Chain rule Product rule Derivative

    Homework Statement (2x^2 - 3x + 1)(4x^3 + 4x -3)^5 Homework Equations The Attempt at a Solution
  13. B

    How to Differentiate Complex Functions Using Product and Chain Rules?

    Hi 2 questions having a mental block and can't figure them out any help would be apprieciated Q1 differentiate f(x)=ax(2x+b)^7 where a and b are constants Q2 differentiate f(x)=(x^2+cos^3(x^4))^10 thanks for any help cheers
  14. qspeechc

    Understanding the Product Rule to \nabla × (A×B)

    Hello everyone. I'm trying to get my head around this product rule: \nabla \times (A\times B) = (B\cdot \nabla )A - (A\cdot \nabla )B + A(\nabla \cdot B) - B(\nabla \cdot A) Ok, we have this \nabla = (\partial /\partial x,\partial/\partial y,\partial /\partial z) and for dot...
  15. B

    Differentiating y: Product Rule Applied

    Homework Statement Differentiate y = u * e^t + v * t * e^t Homework Equations Product Rule. The Attempt at a Solution y = u' * e^t + u * e^t + ( v' * t * e^t + v * e^t + v * t * e^t) u and v are functions of t. I forgot whether the product rule works like this: d/dt [xyz] =...
  16. D

    How Do You Determine When to Use the Chain Rule or Product Rule in Calculus?

    I have a question more than a problem to answer. I'm having a difficult time recognizing when to use the product rule and when to use the chain rule. How do you recognize when to use each, especially when you have to use both in the same problem. Problems like y+x^4y^3-5x^6+3y^8-42=0 tend...
  17. S

    Introduction to the product rule

    Homework Statement a) How many bit strings are there of length 8? b) How many bit strings are there of length 8 which begins with 2 1's? Homework Equations Product Rule The Attempt at a Solution a) Since a bit string is either 0 or 1 there are two possibilities for each one...
  18. E

    Derivatives. Product rule with 3 products

    Homework Statement If f(x) = (3 x )(sin x) (cos x), find f'( x ). A question I have is , is there anything special to do when you have 3 products instead of 2 The Attempt at a Solution Well I used the product rule as if am multipling (3xsinx) (cosx) but that doesn't...
  19. S

    Product rule for derivatives of operators

    I ve been trying to derive this for some time now. The rule is similar to the one for simple math derivatives. d/dx(A^B^)=dA^/dx B^ + A^ dB^/dx Is the derivation on similar lines. Any directions??
  20. F

    Understanding the Product Rule: A Closer Look at Solving y=2x(1-x)^2

    Homework Statement y=2x(1-x)^2 Homework Equations The Attempt at a Solution y=2x(1-x)^2 y`=-x ----------------- (1-x)^1/2 I thought i was done here. The book takes a few more steps. it adds: -x ----------------- (1-x)^1/2 to this: 2(1-x)^1/2...
  21. F

    Understanding the Product Rule: Common Factor Simplification Confusion Explained

    I've already done the problem (here is the last part, sorry for crappy pic) My question; if I multiply both sides of the + by x^2(x+1) / x^2(x+1) as the common factor to simplify the equation, then why does on of the x^2(x+1) disappear from the numerator in the final answer? It appears as...
  22. J

    Exploring the Product Rule: Why Does It "Go Away"?

    We covered the product rule in maths last lecture, and as part of the derivation of it, we got this line: \frac{\partial y}{\partial x}=\frac{u \partial v}{\partial x} + \frac{v \partial u}{\partial x} + \frac{\partial u \partial v}{\partial x} And were told that as x \rightarrow 0...
  23. D

    Trouble using the chain rule product rule and quotient rule

    im having a lot of trouble using the chain rule product rule and quotient rule..i can do them fine seperatly but when they're put together i can't get them like if you have (x^2-1)^4 (2-3x) i would start with 4(x^2-1)^3(2x)(2-3x)+(x^2-1)^4(-3) have i done something wrong here because i never...
  24. R

    Solve Product Rule Problem: f(8)=7, g(8)=5, f'(8)=-4, g'(8)=6

    If f(8) = 7, g(8) = 5, f '(8) = -4, and g '(8) = 6, find the following numbers. (a) Find (f + g)'(8). i was tryig to apply the product rule to this by doing (f+g)(8)'+(f+g)'(8)...so 0+(f+g)'(8)...so that would be (-4+6)8...but that is not the right way to do it... please help me...
  25. B

    Standard Product Rule: Explained

    Hi, I'm having trouble following the following derivation I have seen in a textbook: The derivation goes as follows: L0P3+L1P2+L2P1=0 This is a Poisson eqn for P3 with respect to L0 which requires <L1P2+L2P1>=0 <L2>=L(BS)(sigma) <L1P2>=.5<L1.phi(y)>.x^2. d^2P0/dx^2 thus...
  26. P

    Proving the Product Rule for Differentiating x^n-1

    Homework Statement Use the product rule to show that dx^n-1/dx = (n-1)x^n-2 Homework Equations The general idea is.. If: h(x) = f(x)g(x) Then: dh(x)/dx = f(x)dg(x)/dx + g(x)df(x)/d(x) The Attempt at a Solution It seems like a simple solution but everytime I attempt solving it...
  27. P

    Parallel vectors and scalar product rule

    hey, ive been given a problem where vector a = 2i + 3j and vector b = \lambdai + 12j and also told that these vectors are parallel of each other. i understand since the vectors are parallel of each other, the angle between them would be equal to zero, thus i could apply the scalar product rule...
  28. tony873004

    Product rule. what did I do wrong?

    It's been too long since I've had an algebra class, so I start getting into trouble as these calculus questions rely more and more on algebra. \begin{array}{l} y = (4x - 5)^4 \,(3x + 1)^5 \\ {\rm{Find the first derivative}}{\rm{. Simplify if possible (i}}{\rm{.e}}{\rm{...
  29. F

    Product rule instead of quotient rule?

    Say for example, to differentiate x/(x²+1) I would use to quotient rule. However, would it be legal to bring up the denominator to: (x)(x²+1)-¹ and use the product/chain rule instead?
  30. B

    How can the product rule be applied to a function with 3 variables?

    hey there, At the moment at school I'm doing Implicit Differentiation. If i had for Instence 2y'yx + 6x = 0 how can I use the product rule on the first step when there are 3 variables? Cheers- Andy
  31. M

    How is the Product Rule Applied to Derivatives in the Form xy'z'?

    How do I carry out the product rule for xy'z' Is it possible to do the product rule with y'z' and after that multiply it by x?
  32. S

    How to Apply the Product Rule to Find f ' (X) for f(x) = e^{4x}(1-2x)^4?

    A problem which I'm sure is rather simple, however I cannot seem to simplify the equation properly to produce the fully simplified answer as written in my textbook. The problem being. f(x)= e^{4x}{(1-2x)}^4 Find f ' (X) All help is greately appreciated!
  33. U

    Product rule in differentiation help

    \int x sin (2x) dx =? u=2x du=2dx \int \frac{u}{2} sin(u) \frac{du}{2} \frac{1}{4} \int usin(u)du \frac{1}{4} (\frac{u^2}{2}sin(u)+u(-cos(u))) \frac{2x^2}{4} sin(2x)-\frac{1}{2} cos(2x)+C is this correct?
  34. F

    Understanding the Product Rule in Calculus: Solving for y = x ln x

    y = x ln x \frac{dy}{dx} = \frac{1}{x ln x} \cdot 1 Is that correct?
  35. F

    Power rule and product rule problem

    (2x+3)^3(x-4) How do I differentiate this?
  36. P

    Understanding the Product Rule: Deriving and Proving Its Validity

    Hi all! I've been working with differentiation for quite some time now, and I know how to use the product rule. f(x) = u(x)*t(x) f'(x) = u'(x)*t(x) + t'(x)u(x) But what I don't understand is how one derives it... :cry: Oh, and one more thing. How do we know a number is irrational...
  37. Z

    Combining product rule with chain rule

    Hey what's up, The problem is...find the derivative of: y= x^2 sec(x-5) My question is...Would I start off by using the product rule and combine the chain rule with it, with x-5 being the inner function and sec(u) being the outer function? thanks...
  38. C

    Differentation Problem (involves product rule)

    Here's the equation: F(x) = (x-1)(x-2)(x-3) I know how to diff. using the product rule when you only have 2 equations, but not 3.I looked at the examples in my book and none of them show how you would work out this sort of problem. So if someone could give me the basic overview of how to...
  39. S

    Applying the Product Rule to a Non-Differentiable Function

    Can the product rule be applied if one of the functions is not differentiable? For example, f(x)={g(x)sin(1/x), x not =0 =0, x=0 where g(0)=g'(0)=0. f'(0)=g'(0)sin(1/0) + g(0)dsin(1/x)/dx =0sin1/0+0dsin(1/x)/dx=0? applying the limit definition, I get f'(0)=g'(0)lim sin(1/h) where...
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