sin10°+sin50°=sin(30°-20°)+sin(30°+20°)=sin30°cos20°-cos30°sin20°+sin30°cos20°+cos30°sin20°=2sin30°cos20°=cos20°cos10°+cos50°=cos(30°-20°)+cos(30°+20°)=cos30°cos20°+sin30°sin...