Ответ:

Объяснение:sin²12=(1-cos24)/2

cos²π/18=(1+cosπ/9)/2

4cos²π/8 -2=2(2cos²π/8-1)=2·cosπ/4=2·√2/2=√2.

3-2sin²(-15°)=3-2sin²15°=3-(1-cos30°)=3-1+cos30°=2+√3/2.

(1+cosβ)(1-cosβ)=1-cos²β=sin²β.

sin²β/(1+cosβ)=(1-cos²β)/(1+cosβ)=(1-cosβ)(1+cosβ) /(1+cosβ)=1-cosβ.