Question

sin(θ+75°)+cos(θ+45°)-cos(θ+15°)的值等于(    )

A.             B.             C.              D.0

Answer 1

解析：sin(θ+75°)+cos(θ+45°)-cos(θ+15°)

=sin(θ+15°+60°)+cos(θ+15°+30°)-cos(θ+15°)

=sin(θ+15°)cos60°+cos(θ+15°)sin60°+cos(θ+15°)cos30°-sin(θ+15°)sin30°-cos(θ+15°)

=sin(θ+15°)+cos(θ+15°)+cos(θ+15°)-sin(θ+15°)-cos(θ+15°)=0.

答案：D