cos(tan^-1(-8/15)+tan^-1 (-12/5))

A: Solution is given below:

A: It is a standard derivative formula, whose derivation can be found mentioned below.

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A: the value of sin^2(21degrees)+cos^2(21 degrees) - sin(70degrees)/cos(20degrees

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A: sin(sin^-1(1/6)+tan^-1(-5))

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A: We know that  cos(A+B)=cosAcosB-sinAsinB Therefore cos(3x)=cos(2x+x)=cos(2x)cos(x)-sin(2x)sin(x)

A: Giventan-1(tan(4))

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