已知tanα2=3,求cos(π2+α)=______.-数学

题目简介

已知tanα2=3,求cos(π2+α)=______.-数学

题目详情

已知tan
α
2
=3
,求cos(
π
2
+α)
=______.
题型:填空题难度:偏易来源:不详

答案

cos(class="stub"π
2
+α)
=sinα=2sinclass="stub"α
2
cosclass="stub"α
2
=
2sinclass="stub"α
2
•cos class="stub"α
2
sin2class="stub"α
2
+cos2class="stub"α
2
=
2tanclass="stub"α
2
1+tan2class="stub"α
2
,把tanclass="stub"α
2
=3
 代入可得
cos(class="stub"π
2
+α)
=class="stub"6
1+9
=class="stub"3
5

故答案为:class="stub"3
5

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