Question

高一数学化简求值

高一数学化简求值：sin200°sin260°+cos200°cos(-260°)
1.sin200°sin260°+cos200°cos(-260°)
2.cos(15°-a)sin15°-sin(165°+a)cos(-15°)

Answer 1

1、原式＝-sin20*(-sin80)+(-cos20)*(-cos80)
=sin20sin80+cos20cos80
=cos(80-20)
=cos60
=1/2
2、原式＝cos(15-a)sin15-sin(15-a)cos15
=sin(15-15+a)
=sina