Finding the points on an ellipse where the slope of the tangent line equals 1

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Discussion Overview

The discussion revolves around finding the points on the ellipse defined by the equation x²/9 + y²/16 = 1 where the slope of the tangent line equals 1. Participants explore the mathematical approach to solving this problem, including the derivative of the ellipse and substitutions into the equation.

Discussion Character

  • Mathematical reasoning

Main Points Raised

  • One participant states the equation of the ellipse and the derivative for the slope of the tangent line as dx/dy = -16x/9y, expressing confusion about how to find points where the slope equals 1.
  • Another participant corrects the derivative to dy/dx = -16x/9y and suggests substituting the slope value into the equation to find a relationship between x and y.
  • A further reply indicates an attempt to substitute y in terms of x into the ellipse equation but arrives at a contradictory result, questioning the validity of the approach.
  • One participant notes that the thread is a duplicate of another post and indicates the intention to close the discussion.

Areas of Agreement / Disagreement

There is no consensus reached regarding the solution to the problem, and the discussion remains unresolved with differing approaches and corrections presented.

Contextual Notes

The discussion includes potential misunderstandings of the derivative and the substitution process, as well as an unresolved contradiction in the mathematical steps taken.

delriofi
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If there is an an ellipse x^2/9 + y^2/16 = 1, and the slope of the tangent is dx/dy = -16x/9y, how do you find what points at which the slope of the tangent is 1? I have no idea how to answer this and I've been trying for like an hour. Can anyone help me?
 
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Hi delriofi! :smile:

delriofi said:
If there is an an ellipse x^2/9 + y^2/16 = 1, and the slope of the tangent is dx/dy = -16x/9y, how do you find what points at which the slope of the tangent is 1? I have no idea how to answer this and I've been trying for like an hour. Can anyone help me?

Don't you mean dy/dx=-16x/9y ?
Well, since you know the slope is 1, you know that 1=-16x/9y, thus 9y=-16x. Substitute that back into the equation for the ellipse and solve for x (or y).
 
Ok so I did x^2/9 + (-9y/16)^2/16 = 1 and I get that x^2/9 - x^2/9 = 1 but that doesn't make sense does it?
 

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