How to switch from sin wave to cos wave?

Question

Hi there.

I have this equation:

$$650 \sin ( \frac {2\pi}5(t-0.75))+1100$$

If I want to change it to a cos graph, waht would I do. I remember I have to do 1/4 times something, but I can't remember what to times it to!

The period of the graph is 5 years. Max is 1750, min 450, the first maximum is 2 years.

Thanks

Answer 1

Note that

$$\sin \theta=\cos \left(\frac{\pi}2-\theta\right)$$