33)cos²73°+cos²47°+cos73°•cos47°=
cos73°(cos73°+cos47°)+cos²47°=
cos73°•2cos60°•cos13°+cos²47°
=cos73°•cos13°+cos²47°=
1/2(cos86°+cos60°)+cos²47°=
1/2cos(90°-4°)+1/4+(1+cos(90°+4°))/2
=1/2sin4°+1/4+1/2+1/2*(-sin4°)=
1/4+1/2=3/4
37)cos²165°-sin²165°=
cos(2•165°)=cos330°
=cos(360°-30°)=
cos30°=√3/2
36)(cos²68°-cos²38°)=
1/2(1+cos136°)-1/2(1+
cos76°)=cos136°-cos76°
=-2•sin106°•sin30°=
-sin106°
-sin106°/sin106°=-1