已知tanα=-1/2,求sin(α-7π)cos(α+5π).
人气:403 ℃ 时间:2020-04-01 15:48:29
解答
∵tanα=-1/2==>sinα/cosα=-1/2∴cosα=-2sinα∵(sinα)^2+(cosα)^2=1==>(sinα)^2+(-2sinα)^2=1∴(sinα)^2=1/5故sin(α-7π)cos(α+5π)=(-sinα)(-cosα)=sinα*cosα=sinα(-2sinα)=-2(sinα)^2=-2(1/5)=-...
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