# Math Help - Acceleration 2

1. ## Acceleration 2

The velocity of a particle starting at the origin is v = (cos2x)^2. Show that acceleration = -4(cos2x)^3 sin2x. When I differentiate v to get acceleration, i do not get the cubed part. Please help???

2. Originally Posted by Sunyata
The velocity of a particle starting at the origin is v = (cos2x)^2. Show that acceleration = -4(cos2x)^3 sin2x. When I differentiate v to get acceleration, i do not get the cubed part. Please help???
$a = \frac{d}{dt} [\cos(2x)]^2$

$a = 2[\cos(2x)] \cdot [-\sin(2x)] \cdot 2 \cdot \frac{dx}{dt}$

$
a = 2[\cos(2x)] \cdot [-\sin(2x)] \cdot 2 \cdot \cos^2(2x)
$

simplify ...