Relations Between Trigonometric Functions

This applet demonstrated why $sin(180\mathrm{°}+\alpha )=-sin(\alpha )sin(180°+\alpha )=-sin(\alpha )$ and $cos(180\mathrm{°}+\alpha )=-cos(\alpha )cos(180°+\alpha )=-cos(\alpha )$. Click on the boxes to decide whether you want to see the cosine or sine function. Move the sliders to see the relationship between the functions.