已知sin(a+b)sin(a-b)=1/3,求证:1/4sin2a.sin2a+sinb.sinb+cosa.cosa.cosa.cosa为定值.我不会打平方和四次方,只好搞成相乘了~我做的求证的那堆东东等于cosa.cosa+sinb.sinb.前面的推出:(sinacosb+cosasinb)(sinacosb-
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