tan4x =

31

Prove that  

32

cot x cot 2x – cot 2x cot3x – cot3x cotx =1

34

Prove that cos4x   =  1 - 8sin²xcos²x.

35

Prove that cos6x = 32cos⁶ x- 48cos⁴x + 18cos²x-1