sin(-250°)cos70°cos2155°-sin225°的值为()A.-32B.-12C.12D.32-数学

题目简介

sin(-250°)cos70°cos2155°-sin225°的值为()A.-32B.-12C.12D.32-数学

题目详情

sin(-250°)cos70°
cos2155°-sin225°
的值为(  )
A.-
3
2
B.-
1
2
C.
1
2
D.
3
2
题型:单选题难度:偏易来源:烟台二模

答案

因为
sin(-250°)cos70°
cos2155°-sin225°

=class="stub"-sin250°cos70°
cos225°-sin225°

=
-sin(180°+70°)cos70°
cos225°-sin225°

=class="stub"sin70°cos70°
cos 50°

=class="stub"sin140°
2cos 50°

=class="stub"sin40°
2cos 50°

=class="stub"cos50°
2cos 50°

=class="stub"1
2

故选C.

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