Can someone please explain, sin, cos and tan to me??

Brief explanation:

1. all are ratios of sides of a right triangle with two other angles given

2. (sin(t),cos(t)) are the coordinates of a point on the unit circle whose ray from origin to point makes an angle t with the positive x axis. Other functions are derived from these.

3. sin(t) = [e^(it)-e^(-it)]/2i

cos(t) = [e^(it)+e^(-it)]/2

4. sin(t) and cos(t) can be defined by power series

5. sin(t) and cos(t) arise in the solution of the differential equation

y" = -y

Nope

Something you sure as hell will not need in your future.