sin(π2+θ)=13,则cos2θ=______.-数学

题目简介

sin(π2+θ)=13,则cos2θ=______.-数学

题目详情

sin(
π
2
+θ)=
1
3
,则cos2θ
=______.
题型:填空题难度:中档来源:不详

答案

∵sin(class="stub"π
2
)=class="stub"1
3
,∴cosθ=class="stub"1
3

∴cos2θ=2cos2θ-1=2×class="stub"1
9
-1
=-class="stub"7
9

故答案为:-class="stub"7
9

更多内容推荐