Help finding equation of the tangent line to the graph

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Homework Help Overview

The problem involves finding the equation of the tangent line to the implicit curve defined by the equation x^2 - xy + y^2 = 19 at the point (3, -2). The subject area pertains to implicit differentiation and the application of derivatives in the context of tangent lines.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the process of implicit differentiation, particularly focusing on the derivative of the term -xy and the application of the product rule. There are attempts to substitute specific values into the derived equations to find the slope of the tangent line. Questions arise regarding the correct application of differentiation rules and the resulting expressions.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the differentiation process. Some guidance has been offered regarding the use of the product rule, but there is no explicit consensus on the correct approach or resolution of the problem yet.

Contextual Notes

Participants express uncertainty about the differentiation of specific terms and the implications of their calculations on the final answer. There is a recognition of potential errors in applying the product rule, which is a key aspect of the discussion.

hauk-gwai
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Homework Statement


Find the equation of the tangent line to the graph of x^2 - xy + y^2 = 19 (where y=y(x)) at (3,-2).


Homework Equations





The Attempt at a Solution



So, this is what I did:
d/dx(x^2-xy+y^2) = (19)d/dx

2x*dx/dx-dy/dx+dy/dx+2y(dy/dx)=0

2x+2y(dy/dx)=0

And I am stuck, the answer to this question is:
y+2=8/7(x-3)

and I don't know how to get the slope.
 
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Well you have your values of x and y, (3,-2). Sub that into the 2x+2y(dy/dx)=0 you got to solve for dy/dx, then you have the gradient of the tangent. Now use the gradient-point form of a straight line to find the equation of the tangent.
 
hauk-gwai said:

Homework Statement


Find the equation of the tangent line to the graph of x^2 - xy + y^2 = 19 (where y=y(x)) at (3,-2).


Homework Equations





The Attempt at a Solution



So, this is what I did:
d/dx(x^2-xy+y^2) = (19)d/dx

2x*dx/dx-dy/dx+dy/dx+2y(dy/dx)=0
d(x^2)/dx= 2x and d(y^2)/dx= 2y(dy/dx) but d(-xy)/dx is NOT -dy/dx+ dy/dx!

2x+2y(dy/dx)=0

And I am stuck, the answer to this question is:
y+2=8/7(x-3)

and I don't know how to get the slope.
 
I am pretty sure I got the x^2 and the y^2 part right.

I am just having trouble taking the deriv of the bolded part:
x^2-xy+y^2=19

Do I apply the product rule for the d/dx(-xy)?
 
Yes! It's a product, isn't it?
 
Yeah, but the thing is, I tried applying the product rule, and my results were different, I answer did not match with the answer key, so somewhere within the product rule, I screwed up somewhere, so how do you take d/dx(-xy)?
 
The product rule:
d/dx(u v)
= (du/dx) v + u (dv/dx)

In this case, uv = xy, so ... ?
 

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