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

  • question_answer
    \[\tan 20{}^\circ +\tan 40{}^\circ +\sqrt{3}\tan 20{}^\circ \tan 40{}^\circ =\]

    A) \[\frac{1}{\sqrt{3}}\]

    B) \[\sqrt{3}\]

    C) \[-\frac{1}{\sqrt{3}}\]

    D) \[-\sqrt{3}\]

    Correct Answer: B

    Solution :

    We know that \[\tan \,({{20}^{o}}+{{40}^{o}})=\frac{\tan \,{{20}^{o}}+\tan \,{{40}^{o}}}{1-\tan \,{{20}^{o}}\,\tan \,{{40}^{o}}}\] \[\Rightarrow \,\,\,\sqrt{3}=\frac{\tan \,{{20}^{o}}+\tan \,{{40}^{o}}}{1-\tan \,{{20}^{o}}\,\tan \,{{40}^{o}}}\] \[\Rightarrow \,\,\sqrt{3}-\sqrt{3}\,\tan \,{{20}^{o}}\,\tan \,{{40}^{o}}=\tan \,{{20}^{o}}+\tan \,{{40}^{o}}\] \[\Rightarrow \,\,\tan \,{{20}^{o}}+\tan \,{{40}^{o}}+\sqrt{3}\,\tan \,{{20}^{o}}\,\tan \,{{40}^{o}}=\sqrt{3}.\]


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