- #1
phil ess
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Homework Statement
A spaceship moves along y = x3 - 8x in the positive x-direction. Shutting off the engines at P allows it to move off along the tangent at P. Find P so that the ship can reach the point (4,0).
Homework Equations
Dunno
The Attempt at a Solution
So I start with P = (x1,y1). The slope of the tangent is then m = 3x12 - 8 from the first derivative.
Then I need P, so I went like this:
m = (y2 - y1) / (x2 - x1) = 3x12 - 8 where y2 and x2 are (4,0).
But now I have 1 Eqn. and 2 variables so I can't solve. I was thinking of using y = mx + b because I have y and x, plus an equation for m but then I end up with 2 equations and 3 variables because of the b term. Please help!