Trigonometric Functions

Prove the following:-
22. cot x cot 2x – cot 2x cot 3x – cot 3x cot x = 1
23.
2
2 4
4tan (1 tan ) tan 4
1 6 tan tan
x x
x
x x
−
=
− +
24. cos 4x = 1 – 8sin2
x cos2
x
25. cos 6x = 32 cos6
x – 48cos4
x + 18 cos2
x – 1