__a=1/2

__b=-8

__a=-1/2

__b=8

__a=-20

- February 12th 2008, 01:06 PMplstevensFor what values of a and b is the line 4x + y = b tangent to the parabola y = ax2 wh
__a=1/2

__b=-8

__a=-1/2

__b=8

__a=-20 - February 12th 2008, 03:02 PMJhevon
- February 12th 2008, 06:36 PMplstevens
the wh, should be when x=4, and the a's and b's are th choices that i was given

- February 12th 2008, 07:51 PMtopsquark
Well, given the parabola , what is the equation of the line tangent to it at x = 4?

The tangent line must pass through the point (4, 16a).

, so when x = 4 the slope of the tangent line is .

So the equation of the line that passes through the point (4, 16a) that has a slope of 8a is:

Insert the point (4, 16a) to find b:

So the tangent line is or in the form given in the problem:

Compare this with

What are your values for a and b?

-Dan