Prove that cos−1(1312)+sin−1(53)=sin−1(6556).Answer: Proved.SolutionConvert the cosine term: if cosα=1312 then sinα=135, so cos−11312=sin−1135.LHS=sin−1135+sin−153Apply sin−1a+sin−1b=sin−1(a1−b2+b1−a2) with a=135, b=53:=sin−1(135⋅54+53⋅1312)=sin−1(6520+36)=sin−16556cos−11312+sin−153=sin−16556CBSE Class 12 Board · 2010 · Subjective