dy/dx = 6x^2 - 6x - 6
= 0 for a horizontal slope
x^2 - x - 1 = 0
x = (1 ± √5)/2
= appr 1.618 or -.618
you are correct, but all it asked for is the values of x
(did you know that the first answer x = 1.618.. is the "golden ratio " ? )
2. For what values of x dies the graph of f(x)=2x^3-3x^2-6x+87 have a horizontal tangent?
My answer:
(1.6,77.9)
(-0.62, 89.1)
1 answer
1 answer