We show the sine in the unit circle. The unit circle is a circle with radius .

The hypotenuse of the triangle in the unit circle has a length of 1. In this case sine is equal to the opposite:

The sine function is the length of the opposite with regards to the angle . One can easily observe that:

(1)  

This is the plot of the sine function between 0 and :

Here are some values of the sine functions that are worth remembering:

Alpha in degree	Alpha in radians	Value of sine of alpha