Question

sin75°cos105°-sin105°sin15°的值等于

Answer 1

原式=sin75cos(180-75)-sin(180-75)sin(90-75)
=sin75(-cos75)-sin75cos75
=-sin75cos75-sin75cos75
=-2sin75cos75
=-sin150
=-1/2

Answer 2

sin75°cos105°-sin105°sin15°
=-sin75°sin75°-cos75°cos75°
=-(sin²75°+cos°75°)
=-1