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将θ=a;且将分子分母都剩以cos(a/2)则
f(θ)=f(a)=-1/2+sin(5a/2)/2sin(a/2)=-1/2+sin(5a/2)*cos(a/2)/sina
将cos(a/2)*sin(5a/2)=sin(2a)+sin(3a)由积差化和得。
所以f(a)=2cos(a)+3*cos(a) *cos(a)-3/2
f(θ)=f(a)=-1/2+sin(5a/2)/2sin(a/2)=-1/2+sin(5a/2)*cos(a/2)/sina
将cos(a/2)*sin(5a/2)=sin(2a)+sin(3a)由积差化和得。
所以f(a)=2cos(a)+3*cos(a) *cos(a)-3/2
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