1)sin87°-sin59°-sin93°+sin61°=sin(90°-3°)-
sin(90°+3°)-(sin59°-sin61°)=cos3°-cos3°-
2*sin1°•cos90°=0
2)sin10°•sin20°•sin70°•
sin80°=sin10°•sin(90°-10°)
•sin20°•sin(90°-20°)=
sin10°•cos10°•sin20°•
cos20°=1/4•sin20°•sin40°
=1/4*sin(90°-70°)•
sin(90°-50°)=1/4*cos70°•
cos50°