Prove that 2tan−1(21)+tan−1(71)=tan−1(1731).Answer: Proved.SolutionFirst, 2tan−121=tan−11−412⋅21=tan−13/41=tan−134.Then add tan−171:tan−134+tan−171=tan−11−34⋅7134+71=tan−12121−42128+3=tan−117312tan−121+tan−171=tan−11731CBSE Class 12 Board · 2011 · Subjective