10th Class Mathematics Introduction to Trigonometry Question Bank MCQs - Introduction to Trigonometry

  • question_answer
    Given that \[\sin \theta =\frac{a}{b},\]then \[\cos \theta \] is equal to: (NCERT EXEMPLAR)

    A) \[\frac{b}{\sqrt{{{b}^{2}}-{{a}^{2}}}}\]

    B) \[\frac{b}{a}\]

    C) \[\frac{\sqrt{{{b}^{2}}-{{a}^{2}}}}{b}\]

    D) \[\frac{a}{\sqrt{{{b}^{2}}-{{a}^{2}}}}\]

    Correct Answer: C

    Solution :

    [c] Given, \[\sin \theta =\frac{a}{b}\]
    \[\cos \theta =\sqrt{1-{{\sin }^{2}}\theta }\] \[[{{\sin }^{2}}\theta +{{\cos }^{2}}\theta =1]\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\cos \theta =\sqrt{1-{{\left( \frac{a}{b} \right)}^{2}}}=\sqrt{1-\frac{{{a}^{2}}}{{{b}^{2}}}}=\frac{\sqrt{{{b}^{2}}-{{a}^{2}}}}{b}\]


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