# Trigonometry..

posted by
**Lg** on
.

During high tide the water depth in a harbour is 22 m and during low tide it is 10m(Assume a 12h cycle).

Calculate the times at which the water level is at 18m during the first 24 hours.

My solution:

first I found the cos equation: H(t)=-6cos(π/6t)+16

then..

Let π/6t=Θ

18=-6cosΘ+16

18-16=-6cosΘ

Θ=1.230959417

Then I don't know what's next....