How Large is x(t) at Maximum Acceleration for an Oscillating Block?

[shadowice]

Homework Statement

A 18.0-kg block oscillates back and forth along a straight line on a frictionless horizontal surface. Its displacement from the origin is given by
x(t) = (17.0 cm) cos[( 22.0 rad/s) t + π rad]

What is the magnitude of x(t) when the block experiences its maximum acceleration?

Homework Equations

most are below

The Attempt at a Solution

i started to work backwords and solve for k but after that I am lost since i thought k is what i should be solving for

nm just realized it gave it to me in the problem you can delete this

 

[rl.bhat]

What is the magnitude of x(t) when the block experiences its maximum acceleration?
When the acceleration is maximum, x(t) is maximum i.e. a

 

[shadowice]

ya the original eq had it as the very first term it was 17cm