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

  • question_answer
    If \[\tan A-\tan B=x\] and \[\cot B-\cot A=y,\]then \[\cot (A-B)=\]

    A) \[\frac{1}{x}+y\]

    B) \[\frac{1}{xy}\]

    C) \[\frac{1}{x}-\frac{1}{y}\]

    D) \[\frac{1}{x}+\frac{1}{y}\]

    Correct Answer: D

    Solution :

    \[\cot \,(A-B)=\frac{1}{\tan \,(A-B)}=\frac{1+\tan A\,\,\tan B}{\tan A-\tan B}\] \[=\frac{1}{\tan A-\tan B}+\frac{\tan A\,\,\tan B}{\tan A-\tan B}=\frac{1}{x}+\frac{1}{y}\].


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