Find dy/dx at the point (-3, 1) for the equation x = y^3-9y^2+5.

Question

A. -1/17
B. -1/13
C. -1/15
D. 1/17
E. 1/15

I posted this question before with a typo, but the point still doesn't appear to be on the graph of the function.

Answer 1

yes it is. Perhaps you are misled by the x being the independent variable instead of y
When y = 1
x = 1^3 = 9 (1)^2 + 5
= 1 - 9 + 5
= -3 sure enough
now the problem

dx/dx = 1 = 3 y^2 dy/dx - 18y dy/dx

1 = (3y^2-18y)dy/dx
dy/dx = 1/ (3*1^2 -18*1)
dy/dx = 1/(-15) = -1/15
amazing - that is one of the choices !

Answer 2

Sometimes conventional obscurity is insufficient and extraordinary efforts must be made to confuse the student. One seemingly simple but surprisingly effective technique is to reverse the usual roles of x and y.

Answer 3

Haha! Thank you!

Answer 4

You are welcome.