Question

If y = 2x^3 - 4x and dx/dt = 4, find dy/dt when x = 1. Give only the numerical answer. For example, if dy/dt=3, type only 3.

Answer 1

dy/dt = 8

Explanation:

y = 2x^3 -4x

dy/dt = 2 * 3x^2 dx/dt -4 dx/dt

dy/dt = 6x^2 dx/dt - 4 dx/dt

substitute dx/dt =4 and x=1

dy/dt = 6 * (1)^2 * 4 - 4(4)

dy/dt = 24-16

dy/dt = 8