1) tg 2x=ctg x

2) cos x=cos 2x-cos 3x

2) (cosx+co3x) - cos2x-0

2cos2xcosx-cos2x-0

cos2x (2cosx-1) = 0

cos2x=0, 2x=π/2+πn, x=π/4+πn/2

cosx=1/2, x = + - π/3+2πn

1) 2tgx / (1-tg²x) = 1/tgx

2tg²x=1-tg²x

3tg²x=1

tg²x=1/3

tgx = + - 1/√3

x = + - arctgx1/√3+πn