sin^2 15°-cos^2 15°的值是A.-√3/2 B.1/2 C.-1/4 D.3/4

问题描述:

sin^2 15°-cos^2 15°的值是
A.-√3/2 B.1/2 C.-1/4 D.3/4

=-cos30°
=-√3/2

A

原式=-(cos^2 15°-sin^2 15°)
=-cos30度
=-√3/2
选A