化简cos15°cos45°-cos75°sin45°的值为（）A．12B．32C．-12D．-32

Question

化简cos15°cos45°-cos75°sin45°的值为（　　）

A．(1)/(2)
B．(√(3))/(2)
C．-(1)/(2)
D．-(√(3))/(2)

(1)/(2)
B．(√(3))/(2)
C．-(1)/(2)
D．-(√(3))/(2)(1)/(2)1122
(√(3))/(2)
C．-(1)/(2)
D．-(√(3))/(2)(√(3))/(2)√(3)√(3)√(3)

3

322
(1)/(2)
D．-(√(3))/(2)(1)/(2)1122
(√(3))/(2)(√(3))/(2)√(3)√(3)√(3)

3

322

Answer 1

cos15°cos45°-cos75°sin45°
=cos15°cos45°-sin15°sin45°
=cos（15°+45°）=cos60°=(1)/(2)
故选A． (1)/(2)111222
故选A．