三角函数 (11 16:41:22)已知2sina=cosa,求2sin2a+3sinacosa-cos2a的值
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三角函数 (11 16:41:22)已知2sina=cosa,求2sin2a+3sinacosa-cos2a的值
三角函数 (11 16:41:22)
已知2sina=cosa,求2sin2a+3sinacosa-cos2a的值
三角函数 (11 16:41:22)已知2sina=cosa,求2sin2a+3sinacosa-cos2a的值
2sin2a+3sinacosa-cos2a
= 4sinacosa+3sinacosa-(cosa2-sina2)
=sina2-cosa2+7sinacosa
因为2sina=cosa
所以原式就= sina2-4sina2+7sina*2sina
=11sina2