Question

Sinusoidal functions
A pendulum is swinging back and forth. After t seconds, the horizontal distance from the bob to the place where it was released is given by H(t)=7−7cos( 2π(t−2)/20). How often does the bob cross its midline?

Answer 1

it crosses the midline twice each period.
H(t)=7−7cos( 2π(t−2)/20)
cos(2π(t-2)/20) = cos(π/10 (t-2))
So the period is 2π/(π/10) = 20 seconds
It crosses the midline every 10 seconds

Answer 2

If it were Sin, how many times would it cross midline? 3?