C-09-Q099mediumsingle_mcqcosecAcosecA−1+cosecAcosecA+1=?\dfrac{\operatorname{cosec} A}{\operatorname{cosec} A - 1} + \dfrac{\operatorname{cosec} A}{\operatorname{cosec} A + 1} = ?cosecA−1cosecA+cosecA+1cosecA=?a2sec2A2\sec^2 A2sec2Ab2cosec2A2\operatorname{cosec}^2 A2cosec2Ac2tan2A2\tan^2 A2tan2Ad2cot2A2\cot^2 A2cot2Aব্যাখ্যাOver a common denominator the numerators add to cosecA(cosecA+1)+cosecA(cosecA−1)cosec2A−1=2cosec2Acot2A\dfrac{\operatorname{cosec} A(\operatorname{cosec} A+1) + \operatorname{cosec} A(\operatorname{cosec} A-1)}{\operatorname{cosec}^2 A - 1} = \dfrac{2\operatorname{cosec}^2 A}{\cot^2 A}cosec2A−1cosecA(cosecA+1)+cosecA(cosecA−1)=cot2A2cosec2A. Since cosec2A=1+cot2A\operatorname{cosec}^2 A = 1+\cot^2 Acosec2A=1+cot2A... evaluating gives 2cosec2Acosec2A−1=2/sin2Acos2A/sin2A=2cos2A=2sec2A\dfrac{2\operatorname{cosec}^2 A}{\operatorname{cosec}^2 A - 1} = \dfrac{2/\sin^2 A}{\cos^2 A/\sin^2 A} = \dfrac{2}{\cos^2 A} = 2\sec^2 Acosec2A−12cosec2A=cos2A/sin2A2/sin2A=cos2A2=2sec2A.