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

  • question_answer
    \[\tan 100{}^\circ +\tan 125{}^\circ +\tan 100{}^\circ \tan 125{}^\circ =\] [DCE 1999]

    A) 0

    B) 1/2

    C) -1

    D) 1

    Correct Answer: D

    Solution :

    \[\tan \,({{100}^{o}}+{{125}^{o}})=\frac{\tan \,{{100}^{o}}+\tan \,{{125}^{o}}}{1-\tan \,{{100}^{o}}\,\tan \,{{125}^{o}}}\] \[\therefore \]\[\tan \,{{225}^{o}}=\frac{\tan \,\,{{100}^{o}}+\tan \,\,{{125}^{o}}}{1-\tan \,{{100}^{o}}\,\tan \,{{125}^{o}}}\] i.e., \[1=\frac{\tan \,{{100}^{o}}+\tan \,\,{{125}^{o}}}{1-\tan \,\,{{100}^{o}}\,\tan \,\,{{125}^{o}}}\] i.e.,\[\tan {{100}^{o}}+\tan {{125}^{o}}+\tan {{100}^{o}}\tan {{125}^{o}}=1.\]


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