求值 sin(-1320°)cos1110°+cos(-1020°)sin750°+cos495°
问题描述：
求值 sin(-1320°)cos1110°+cos(-1020°)sin750°+cos495°
答
利用诱导公式，原式=-sin60*cos30+cos60*sin30+cos135=-sin30-cos45
答
sin(-1320°)cos1110°+cos(-1020°)sin750°+cos495°
=sin(-180x8+120)cos(180x6+30)+cos(-180x6+60)sin(4x180+30)+cos(2x180+135)
=sin120cos30+cos60sin30+cos135
=3/4+1/4-√2/2
=1-√2/2