$$\sin30\degree=2\sin15\degree\cos15\degree$$  

$$\sin30\degree=2\sin15\degree\cos45\degree$$  

$$\cos30\degree=\cos^215\degree+\sin^215\degree$$  

$$\cos30\degree=2\cos^215\degree+\sin^215\degree$$  

$$\cos30\degree=2\cos^215\degree-1$$  

$$-\frac{24}{25}$$  

$$-\frac{24}{7}$$  

$$-\frac{7}{25}$$  

$$\frac{7}{25}$$  

$$\frac{24}{25}$$  

$$\frac{219}{236}$$  

$$\frac{240}{289}$$  

$$\frac{120}{289}$$  

$$\frac{64}{119}$$  

$$\frac{32}{129}$$  

-40

-20

8

20

60

$$\frac{2}{p^2+1}$$  

$$\frac{4}{p^2+1}$$  

$$\frac{2p}{p^2+1}$$  

$$\frac{p^2-1}{p^2+1}$$  

$$\frac{1-p^2}{1+p^2}$$