JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Trigonometrical ratios of sum and difference of two and three angles

  • question_answer
    If \[A+B=\frac{\pi }{4},\]then \[(1+\tan A)(1+\tan B)=\]

    A) 1

    B) 2

    C) \[\infty \]

    D) -2

    Correct Answer: B

    Solution :

    Given that \[A+B=\frac{\pi }{4}\,\Rightarrow \,\tan \,(A+B)=\tan \,\frac{\pi }{4}\] \[\Rightarrow \,\,\frac{\tan A+\tan B}{1-\tan A\,\tan B}=1\] \[\Rightarrow \,\,\tan A+\tan B+\tan A\,\tan B=1\] \[\Rightarrow \,\,(1+\tan A)\,(1+\tan B)=2\].


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