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TransendentialPI
 3 years ago
I need to check my work. It is from a "fake" AP Calculus AB 2008 exam.
The line normal to 3x^2+4y+y^2=3
at x = m is parallel to the yaxis. What is m? the choices for the answers are
a. 3
b. 2
c. 0
d. 3
e. 2
I used implicit differentiation to get a derivative of
dy/dx = (6x)/(4+2y)
Won't the slope of the normal line be the neg. recip of this derivative function?
This means
(4+2y)/(6x)
To be parallel to the yaxis, the slope is undefined so 6x = 0 and x = 0.
This means choice c is correct?
TransendentialPI
 3 years ago
I need to check my work. It is from a "fake" AP Calculus AB 2008 exam. The line normal to 3x^2+4y+y^2=3 at x = m is parallel to the yaxis. What is m? the choices for the answers are a. 3 b. 2 c. 0 d. 3 e. 2 I used implicit differentiation to get a derivative of dy/dx = (6x)/(4+2y) Won't the slope of the normal line be the neg. recip of this derivative function? This means (4+2y)/(6x) To be parallel to the yaxis, the slope is undefined so 6x = 0 and x = 0. This means choice c is correct?

This Question is Closed

Puzzhang
 3 years ago
Best ResponseYou've already chosen the best response.1Agreed. Looks correct.

SmoothMath
 3 years ago
Best ResponseYou've already chosen the best response.1I didn't do any of the math, but I read your method and it sounds just perfect. Derive to get the slope, solve for dy/dx. The line normal to this will be the negative reciprocal. For it to be parallel to the y axis, it would have to be undefined. So yeah. Or you could have just known that the line normal would be parallel when the tangent was 0 and solved it that way without taking the negative reciprocal. Both work.

SmoothMath
 3 years ago
Best ResponseYou've already chosen the best response.1Okay, and yeah. I went ahead and checked your implicit differentiation too. That checks out.
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