已知a=(2sin35°,2cos35°),b=(cos5°,-sin5°),则a•b=(  ) A.12 B.1 C.2 D.2sin40°

问题描述:

已知

a
=(2sin35°,2cos35°),
b
=(cos5°,-sin5°),则
a
b
=(  )
A.
1
2

B. 1
C. 2
D. 2sin40°

a
=(2sin35°,2cos35°),
b
=(cos5°,-sin5°),
a
b
=2sin35°cos5°-2cos35°sin5°=2sin(35°-5°)2sin30°=1.
故选:B.