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cos(a+b)=m(cos(a-b) then tan a=?

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    Expand both sides using sum of angles formula:
    cos(a+b)=cos(a)cos(b)-sin(a)sin(b)
    cos(a-b)=cos(a)cos(b)+sin(a)sin(b)

    Divide by cos(a) on both sides and solve for tan(a) to get:

    tan(a)=cot(b)*(1-m)/(1+m)

    Check me.

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