Physics1 
Oct1607 01:48 PM 
Tangent lines
1. The problem statement, all variables and given/known data
A traveler in space is moving left and right on y = x^2. He shuts off the engines and continues on the tangent line until he reaches point (4, 15). At what point on the curve should he shut off the engines to reach that point?
3. The attempt at a solution
Ok, the derivative is 2x. I know have to solve for the slope of the tangent line.
Rise over run = (15a^2) / (4  a)
(a, a^2) is the point to shut off. I get a^2  8a + 15 as the quadratic equation but the value 4 from it isn't correct when I plug it into 2x. What am I doing wrong?
