3cos10°-1sin170°=()A.4B.2C.-2D.-4-数学

题目简介

3cos10°-1sin170°=()A.4B.2C.-2D.-4-数学

题目详情

3
cos10°
-
1
sin170°
=(  )
A.4B.2C.-2D.-4
题型:单选题难度:偏易来源:不详

答案

3
cos10°
-class="stub"1
sin170°
=
3
cos10°
-class="stub"1
sin(180°-10°)

=
3
cos10°
-class="stub"1
sin10°
=
3
sin10°-cos10°
sin10°cos10°

=
2(
3
2
sin10°-class="stub"1
2
cos10°)
sin10°cos10°
=
2sin(10°-30°)
sin10°cos10°

=class="stub"-2sin20°
class="stub"1
2
•2sin10°cos10°
=class="stub"-4sin20°
sin20°
=-4
故选D

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