Find the value of tan−1(yx)−tan−1(x+yx−y).Answer: 4πSolutionUse tan−1A−tan−1B=tan−11+ABA−B with A=yx, B=x+yx−y.Numerator A−B=y(x+y)x(x+y)−y(x−y)=y(x+y)x2+y2.Denominator 1+AB=y(x+y)y(x+y)+x(x−y)=y(x+y)x2+y2.tan−1(yx)−tan−1(x+yx−y)=tan−1(x2+y2x2+y2)=tan−1(1)=4π4πCBSE Class 12 Board · 2011 · Subjective