已知:5sinb=sin(2a+b),求证tg(a+b)/tga=3/2

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已知:5sinb=sin(2a+b),求证tg(a+b)/tga=3/2 因为5sinb=sin(2a+b)所以5sin(a+b-a)= sin(a+a+b)展开得：5sin(a+b)*cosa -5cos(a+b)*sina = sina*cos(a+b)+cosa*sin(a+b)所以　4sin(a+b)*cosa = 6sina*cos(a+b)即　tg(a+b)/tga=3/2