Cos 3a - cos 5a sin 10+ sin 40 cos 20- cos70 sinb-sin 3b cos п/8- сos п/10 sin 2b-sin 3b/cos 2b-cos3b

cos 3a - cos 5a=2sinasin4a
sin 10+ sin 40=2sin25cos15
cos 20- cos70=2sin25sin45=√2sin25
sinB-sin 3B=-2sinbcos2b
cos п/8- сos п/10=-2sin(π/40)sin(9π/40)
sin 2B-sin 3B/cos 2B-cos3B=(-2sin(b/2)cos(5b/2)/(-2sin(b/2)sin(5b/2)=
=ctg(5b/2)

Cos 3a cos 5a=25inasin4a

sin 10+ sin 40=2sin25c0515

cos 20cos70=2sin25sin45=v2sin25 sinB-sin BB=-2sinbcos2b

cos n/8cos n/10=-2in(rr/40)sin(9n/40) sin 2B-sin 3B/cos ZB-cos3B=(-2sin(b/ 2)cos(5b/2)/(-2sin(b/2)sin(5b/2)= =ctg(5b/2)