Question

Find b and c so that y=-13x^3 + bx + c has vertex (2,-8)

Answer 1

b=156, c=-216

Explanation:

we have to obtain two simultaneous equations. the first can be obtained through substitution.

-8=-13(2)^3+2b+c

2b+c=96 ... (1)

the second one is found through differnetiation.

y'=-39x^2+b=0

at x=2, this is satisfied. so,

b=39(2)^2

and so b=156, c=-216