sinA=1/3,求cos2A

问题描述:

sinA=1/3,求cos2A

cos2A
=1-2sin²A
=1-2x(1/3)²
=1-2/9
=7/9

sinA=1/3
A=30度

cos2A
=cos60度
=1/2

不懂可追问,有帮助请采纳,谢谢!

sinA=1/3
则cos2A=1-2sin²A=1-2*(1/3)²=1-2/9=7/9

cos2A=1-2sin^2A
=1-2(1/3)^2
=1-2/9
=7/9