Question

Помогите с решением.

Answer 1

10
-2sin[(a-b-a-b)/2]*cos[(a-b+a+b)/2]/(sina*sinb)=2sinb*cosa/(sina*sinb)=
=2ctga
11
ctg198=ctg(180+18)=ctg18
12
sin1,3π=sin(3π/2-π/5)=-cosπ/5