sin(π\2-α)=1\3 cos(π+2α)等于多少
1个回答
∵sin(π/2-α)=1/3
∴cosα=1/3
∴cos(π+2α)
=-cos2α
=-(2cos²α-1)
=-2cos²α+1
=-2*(1/3)²+1
=7/9
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