Points Definition and 1000 Threads

  1. Nikkki

    I Equation for circle points in 3D

    Hello, I am trying to solve a problem and I would like to ask for help. I have 3 points (A, B, C) in 3D space that are assumed to be on a circle. EXAMPLE 1 EXAMPLE 2 My goal is to create an algebraic formula to calculate the coordinates for 10 points on a circle composed of ABC points at...
  2. J

    I Are Geometric Points Affected By Forces?

    Yesterday I found a playlist of videos by a youtuber "Dialect" who made a distinction between what he called Tier 1 and Tier 2 arguments of Relativity. Tier 2 promoted a view that acceleration was an observer dependent phenomena. In particular he was discussing the Twin Paradox, and he said...
  3. Addez123

    Find all points where surface normal is perpendicular to plane

    a. I solved a but I don't fully understand how it works. $$z = f_x'(1, -1)(x -1) + f_y'(1, -1)(y+1) = 2(x-1) + 3(y+1)$$ Eitherway it's b that's my issue. I can find the gradient of both plane and surface, but trying to do "dot-product of both normals = 1" will give an equation involving two...
  4. curious__

    Find the locus of the points arg((z+1)/(z+2)) = pi

    I tried the following proof and got -2 < x < -1 and y = 0 but my prof said that there should be something else I am missing. I have no idea what that is. Thank you.
  5. Trysse

    I Five points in space with rational distances that are not co-linear

    Hi there, experts on three-D space! while thinking about (physical) space, I have come up with the following (geometry) question: Is it possible to define five points (A, B, C, D, E) in Euclidian space, so that all distances (AB, AC, AD, AE, BC, BD, BE, CD, CE, DE) can be expressed in rational...
  6. Ineedhelpwithphysics

    Speeds of the rolling ball at different points in this roller coaster track

    For this question i tried to reason with my self that C was the fastest and A was the second fastest. B would be the third fastest and D would be the least fastest since the ball has to go up. I looked up the answer and it says that C is the fastest , B and D are equal, and A is the slowest. How...
  7. M

    I An infinity of points on two unequal lines- an intuitive explanation?

    I am familiar with Cantor's work on the concept of infinity and his use of the set theory to explain various types of infinities. Having said that my intuition never seems truly grasp/accept it. Is there a way to train my mind to see this seemingly contradictory situation as a fact? This is...
  8. T

    B Delta-v from Lagrange points to lunar surface?

    What is the delta-v requirements from each of the Earth-Moon lagrange points to landing on the lunar surface? What would be the best software I could use to visualise and calculate that kind of thing? Thanks.
  9. hartmais

    A Can Raoult's Law Determine Boiling Points of Fuel Oil?

    Fuel oil like heavy fuel oil consists of multiple different Carbon and Hydrogen molecule strains. This means that there are a multiple of different boiling points with in the same oil. Cavitation in pumps and valves happen when due to the acceleration of the fluid the pressure drop causing the...
  10. Poetria

    Critical points of a multivariable function (wave equation)

    I would like to check my understanding of this problem. There are the following possibilities: a. Isolated points where the gradient is 0. b. The level curves of height 0 c. The level curves of height 1. d. The level curves of height -1. e. None of the above. I would choose a, c, d. Where...
  11. E

    Finding the potential difference between 2 points in a circuit

    is this method accepted? 2V is split equally between the 2 5kohms resistor because they are of equal resistance. 2V=5kohms 2kohms= 0.8V 3kohms=1.2V. p.d across P and Q= 1V-0.8V=0.2V
  12. W

    I Is there a "Nice" proof that R^2 is not disconnected when we remove 2 points

    Are there "nice" ( without heavy machinery) proofs that ## X:=R^2 - \{p,q\} ## is connected? All I can think is using that path-connectedness implies connectedness. So we consider x,y in X and show there is a path joining them. I am looking for an argument at undergrad level, so that I would not...
  13. mcastillo356

    Calculate (and argue) the critical points of an exponential function

    Hi everybody We can't differentiate ##x^x## neither like a power function nor an exponential function. But ##x^x=e^{x\mbox{ln}x}##. So ##\dfrac{d}{dx}x^x=\dfrac{d}{dx}e^{x\mbox{ln}x}=x^x(\mbox{ln}x+1)## And here comes the doubt: prove the domain of ##x^x## is ##(0, +\infty)## Why is only...
  14. LCSphysicist

    Can Spacelike and Timelike Points Undergo the Same Transformations?

    I want to understand bettew what this statement says. Maybe later we could try to put it mathematically, but for while i want to know if my interpretation is right. When we lie outside the light cone, the physics regarding the limit of the velocity is break, and technically we could go faster...
  15. N

    Collinear Points -- Ways to determine if points are collinear

    Chapter 1, Section 1.1 Collinear Points 59. Three or more points are collinear when they all lie on the same line. Use the steps below to determine whether the set of points {A(2, 3), B(2, 6),C(6, 3)} and the set of points {A(8, 3), B(5, 2), C(2, 1)} are collinear. (a) For each set of points...
  16. M

    Position of the principal points of a telephoto lens system

    Hi everyone, for a lab I need to determine the position of the cardinal points of a telephoto lens. The focal points were determined experimentally, and the focal length given on the lens is 200mm. The principal points should be determined with f=PF. In all the textbooks, the principal points...
  17. I

    B Second derivative and inflection points

    Q: See f(t) in graph below. Does the graph of g have a point of inflection at x=4? There is a corner at x=4, so I don't think there is a point of inflection. Does a point of inflection exist where f''(x) does not exist? The solution says there is a point of inflection, could anyone explain why...
  18. brotherbobby

    The first and second derivatives at various points on a drawn graph

    Problem statement : The function ##y = f(x)## is given above. Question 1 : Locate the points at which the ##\text{first derivative}## of ##y## with respect to ##x## is ##\text{non-zero}##.##\\[5pt]## At points of extrema, like A, C and D, the derivative is zero. Hence the derivative is non...
  19. M

    MHB Points of the surface with minimum distance to the point (3,0,0)

    Hey! :giggle: We have the function $$f(x,y)=(x-3)^2+y^2+(x-y)^2$$ and I have shown that at $(2,1)$ we have a minimum and so $f(2,1)\leq f(x,y)$ for all $(x,y\in \mathbb{R}^2$. I did that in this way: I calculated the gradient and set this equal to zero and found that the only critical point...
  20. K

    B Second derivatives and inflection points

    Hi there. I'm having some trouble wrapping my head around some ideas of inflection points as they relate to the second derivative. I know that an inflection point occurs when f''(x)=0 in most cases. This makes sense to me because at this inflection point the slopes of the tangent change from...
  21. B

    B Are Decimal Points As Significant In Population Dynamics....

    As they are in engineering and manufacturing? I ask because during a very deep, post stroke marbles census in came to light that I had an extraordinarily high level of pattern recognition such that the department head said I was in the top .003 percent of the population. I ran the numbers...
  22. kolleamm

    3d printing materials with different melting points?

    A 3d printer that could print metal and other materials would revolutionize everything. The only problem is that metals have a really high melting point, so if you try to get a metal hot enough to bind to the other metals in its vicinity it would probably destroy the bonds of the neighboring...
  23. Z

    Equilibrium points doubt (ODE system solution)

    Hi. I'm not sure about something related to the equilibrium points (or fixed points) of a non linear ode system solution. As far as I know, to check if an equilibrium point exists, I need to put the function of my ode system equal to zero. Then once the point is found, I can use it to evaluate...
  24. A

    MHB Ryan's Hockey Points: Goals + Assists = 83

    In hockey, the points a player scores is the sum of the goals scored and he assists. In one session, Ryan scored 83 points. Ryan scored 21 fewer goals than assists. a) Write a system of equations to represents the situation. State your variables. b) How many goals and assists Ryan scored in...
  25. I

    Chemistry Melting and boiling points of titanium tetrahalides

    Table boiling point (°C) melting point (°C) TiF4 284 N/A TiCl4 -24 136.5 TiBr4 38 233.5 TiI4 155 377 The solution says that TiF4 is an ionic compound, while TiCl4, TiBr4, and TiI4 are covalent compounds. How would I determine this from the problem without prior...
  26. S

    B Critical points of second derivative

    If the sign on the sign diagram of f" changes from positive to negative or from negative to positive, this means the critical points of f" is non-horizontal inflection of f But what about if the sign does not change? Let say f"(x) = 0 when ##x = a## and from sign diagram of f", the sign on the...
  27. Pipsqueakalchemist

    Engineering Dynamics rigid body question -- Velocity of points on a car's wheel

    The solutions used the spend of the wheel and its radius to find the angular velocity. I’m confused because I thought to find angular velocity you use the speed at the points of the radius not the translation speed of the wheel itself. Can someone explain this to me please
  28. I

    Chemistry Which Structural Isomer Has the Highest Boiling Point?

    Why does the isomer C-C-C-N have the highest boiling point, rather than CC(N)C (where the N is attached to the second carbon)? Isn't N able to form 3 H-bonds in both cases? Thanks.
  29. C

    Can you use Taylor Series with mathematical objects other than points?

    I was recently studying the pressure gradient force, and I found it interesting (though this may be incorrect) that you can use a Taylor expansion to pretend that the value of the internal pressure of the fluid does not matter at all, because the internal pressure forces that are a part of the...
  30. wizzy

    Plotting points evenly around an origin

    Say I have phi starting at 0 and ending at 360 degrees. Theta starts at 0 and ends at 360, and I input 10 points for phi and theta. I am trying to 3d plot phi * theta number of points around a center point. I can plot a coordinate around a sphere using the following, which I think is correct...
  31. F

    A Distance between two uncertain points using haversine?

    Hello everyone. I have two points in space (on the surface of the earth) represented using spherical coordinates (in this case there is no z axis since both are assumed to be at the same height). These points have an associated standard deviation in lambda and in phi, which are longitude and...
  32. M

    Mathematica Extract points from an interpolated curve (not a function)

    Hi PF! I have the given data points here data = {{1.92, 0.74}, {2.32, 1.36}, {2.44, 1.88}, {2.52, 2.08}, {2.68, 1.92}, {2.64, 1.4}, {2.46, 0.78}}; and the following plots the correct interpolation Show[{ListLinePlot[{data}, InterpolationOrder -> 3], ListPlot[\[Lambda]cplx1]}] but...
  33. A

    MHB Proving Triangle Area ≤ $\frac{1}{2}$ in a Square with $(n+1)^2$ Points

    Consider a square with the side of length n and $(n+1)^2$ points inside it. Show that we can choose 3 of them to determine a triangle (possibly degenerate) of area at most $\frac{1}{2}$. I think that I know how to solve the problem for the cases $n=1$ and $n=2$: For $n=1$ we can easily prove...
  34. greg_rack

    B Find Local Max/Min: 2nd Derivative=0

    How do I distinguish between a point of local maxima or minima, when the second derivative in that point is equal to zero?
  35. brotherbobby

    Which points on the plane satisfy the given equation?

    Given the equation : ##|y| x = x##. Two conditions are possible : (1) ##\underline{y\geq 0}## : ##xy = x\Rightarrow \boxed{y = 1}\; (x \neq 0)##. We note that except for zero, ##-\infty<x<+\infty## for this case. (2) ##\underline{y < 0}## : ##-xy = x\Rightarrow \boxed{y = -1}\; (x \neq 0)##...
  36. brotherbobby

    Points on a plane satisfying an equation

    We can write the equation given as ##y+|y| = x+|x|## This has a few conditions. (1) If ##\underline{y\geq 0\; \text{and}\; x\geq 0}##, we obtain ##2y = 2x \Rightarrow \boxed{y = x}##. (2) If ##\underline{y\geq 0\; \text{and}\; x < 0}##, we obtain ##2y = 0 \Rightarrow \boxed{y = 0}##. (3) If...
  37. greg_rack

    Studying non-differentiable points of an irrational function

    I calculated the derivative of this function as: $$\frac{6x^3-4x}{3\sqrt[3]{(x^3-x)^2}}$$ Now, in order to find and later study non-differentiable points, I must find the values which make the argument of the root equal to zero: $$x^3-x=0 \rightarrow x=0 \vee x=\pm 1$$ and then find the left and...
  38. D

    Quickest Route Between Horizontal Points using the Initial Velocity & Friction

    re: https://www.physicsforums.com/threads/is-it-possible-to-solve-for-t.996132/post-6421205 https://www.physicsforums.com/threads/is-it-possible-to-solve-for-t.996132/post-6421230 Would it be possible to find t and r via the exact same equations as found in posts #4 and #10, and then find the...
  39. E

    MHB Is f(x)=ln(x)/x Increasing or Decreasing?

    Find where increasing/decreasing, concavity, local extrema and inflection points for f(x)=ln/x So here is what I have so far: The derivative is 1-ln(x)/x^2 Critical points are (e,1/e) No concavity Local max is also (e,1/e) (no local min) no inflection points Increase on (0, e) and...
  40. Ander99

    Engineering Calculating Equilibrium Points in OVA-Opamp Circuit with Ideal Diodes

    Hi everyone, I need help with this exercise becouse I don't know how to calculate the equilibrium points of a circuit. The original exersice is the following: Assume that the open loop dynamic response of the OVA-opamp gets captured by Fig. 1(a) and consider the circuit of Fig. 1(b). Consider...
  41. D

    Critical points and partial differentiation

    zx = 2xy + y2 -3y = 0 and zy = 2xy + x2 - 3x = 0 Subtracting one equation from the other gives y2 - 3y = x2- 3x ⇒ y (y-3) = x (x-3) This leads to the following solutions ( 0 , 0) , (0 ,3) , (3 , 0) but the answer also gives ( 1, 1) as a solution. What have i done wrong to not get this...
  42. L

    I Probability that two points are on opposite sides of a line

    I want to find the probability that the two points ($x_1, y_1$) and ($x_2, y_2$) lie on the opposite sides of a line passing through the origin $o = (0, 0)$ and makes an angle $\psi$ that is uniformly distributed in $ [0, \pi]$ with the $x$ axis when the angle is measured in clockwise direction...
  43. SchroedingersLion

    A Dense set vs no isolating points

    Greetings, could you commend or correct the following: A dense subset ##X## of a set ##Y## is a set such that in each environment of ##y\in Y##, there is at least one element ##x\in X##. In other words, the elements of ##Y## can be approximated arbitrarily well by elements in ##X##. A set...
  44. L

    MHB Differentiation help (stationary points)

    I’m struggling with questions c, e and f. I don’t think I understand how to find stationary points.
  45. C

    MHB Solve a Quadratic Equation with Vertex Form

    I know this is the equation I have to use a(x - h) 2 + k, but don't know what points to use and how to covert to vertex form
  46. MidgetDwarf

    Verification that ZxZ has no cluster points in RxR

    proof: Assume instead that every point of ℤxℤ is a cluster point. Note that (0,0)∈ℤxℤ. So by assumption, (0,0) is a cluster point of ℤxℤ. ⇒ every neighborhood of (0,0) contains at least one point ℤxℤ different from (0,0). Consider the open ball with center (0,0) and r =1/2, denoted by A. We...
  47. chriscarson

    Decimal points different in these two answers

    I have two answers and somehow the answers have the decimal point in different place. 2445859.873 with the answer of 2.44x106 and 254777070.1 with the answer of 254.6x106 why the teacher do that ?
  48. SSequence

    B Points on a Circle (moving through an obstacle)

    This is a problem in two dimensions. Consider an obstacle (in the form of a line segment) placed at ##x=1##, ##0 \leq y \leq 1##. Now consider the circle of radius ##1## and center at ##(x_0,1)## [initially at time ##t=0##] moving towards right with a combination of: (i) Angular speed of ##2...
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