So make and angle with the measure of 45 degrees. And then label it DOG. It doesn't matter where you start labeling as long as O is your midpoint. :)
In the attachment is a graph of the cosine function that represents changing of the tide.
y max = 10 ft at midnight
y min = 5 ft at 6 AM
For all exponents, (a^n a^m) = a^(n+m)
apply same rules (X^3X^2)/(4*3)
Combine powers. (X^3X^2)/4*3 = X^(3+2)/4*3
X^5/12