AP Calculus: Finding Derivatives, Tangents, and Graph Points

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Discussion Overview

The discussion revolves around finding derivatives, tangent lines, and specific points on the graph of a continuous function defined by the equation x^4 - 5x^2y^2 + 4y^4 = 0. Participants are addressing three main tasks: deriving an expression for the derivative, writing the equation of the tangent line at a specific point, and identifying a point on the graph that does not lie on the tangent line. The scope includes mathematical reasoning and implicit differentiation.

Discussion Character

  • Mathematical reasoning
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant proposes that part A involves taking the derivative and presents an expression for y' as (-4x^3 + 10xy^3) / (-5x^2 2y + 16y^3), expressing uncertainty about its correctness.
  • Another participant suggests that the function should be interpreted as y = f(x) = x^4 - 5x^2y^2 + 4y^2 = 0 and recommends implicit differentiation for part A.
  • A third participant refers to the theorem of implicit functions for finding the derivative and implies that the other two parts should be straightforward once the derivative is established.
  • Several participants confirm the function's correctness and provide guidance on using point-slope form to derive the equation of the tangent line.
  • There is a suggestion to compute dy/dx at points where explicit differentiation is possible, indicating a need for clarity on the derivative's application.
  • Participants discuss using the coordinates (2,1) to find the slope for the tangent line and emphasize the importance of the derivative in determining this slope.

Areas of Agreement / Disagreement

Participants generally agree on the method of implicit differentiation and the use of point-slope form for the tangent line. However, there is no consensus on the correctness of the initial derivative expression provided by the first participant, and some uncertainty remains regarding the next steps in the problem-solving process.

Contextual Notes

There are limitations regarding the assumptions made about the function and the derivative, as well as the potential for multiple interpretations of the tasks. The discussion does not resolve the correctness of the derivative expressions or the subsequent steps needed to complete the problem.

ashleyk
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Let y=f(x) be the continuous function that satifies the equation x^4-5x^2y^2+4y^4=0 and whose graph contains the points (2,1) and (-2,-2). Let 'L' be the tangent to the graph of f(x) at x=2.

A) Find an expression for y'
B) Write an equation for the line 'L'
C) Give the coordinates of a point that is on the graph of f(x) but not the line 'L'


I am assuming part A means to take a derivative (which I did) and got
(-4x^3+10xy^3)/(-5x^2 2y+16y^3) I don't know if this is right but now I am stuck...any help in the right direction would be great! Thanks!
 
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ok I think your function is y = f(x) = x^4 - 5x^2y^2 + 4y^2 = 0. So for art a you want to differentiate implicitly with respect to x. For the second part use point slope for and substitute x = 2. For the third part you know what point is on both graphs? SO give a point which is on f(x) but not on L. For the derivative I got \frac {4x^3 + 10xy^2}{10x^2y + 8y}
 
Last edited:
Is your function:
F(x,y)=x^{4}-5x^{2}y^{2}+4y^{4}

Use the theorem of implicit functions for point "a"...

Daniel.

P.S.Then the other 2 points are easy to solve.
 
dextercoiby has the correct function...any more help would be great...
 
Did u compute the
\frac{dy}{dx}

in the points in which the explicitation is possible...?

Daniel.
 
yes and i got that answer...im just not sure where to go with it now...
 
you know L' is tangent to x = 2. The coordinates are (2,1). Now use point slope form to get the equation.

y-y_1 = m(x-x_1)
 
"m" is the slope in the point (2,1).So if you computed the derivative,the slope is immediate...Then use the formula written by the previous poster to solve point "b",too...

As for point "c",i think it's not that difficult.

Daniel.
 

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