if we draw the terminal point and draw a line to it from the origin we obtain something like this
This can form a right triangle in which we must find the hypotenuse
[tex]\begin{gathered} a^2+b^2=c^2 \\ (\frac{1}{2})^2+(\frac{\sqrt[]{3}}{2})^2=c^2 \\ \frac{1}{4}+\frac{3}{4}=c^2 \\ \frac{4}{4}=c^2 \\ c=\sqrt[]{1} \\ c=1 \end{gathered}[/tex]
the sin is defines as the opposite (y) divided by the hypotenuse, in this case since the hypotenuse is equal to 1, the sin is equal to:
[tex]\frac{1}{2}[/tex]
