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

  • question_answer
    If \[sin\,\theta -\cos \theta =\frac{3}{5},\]the \[\sin \theta .\cos \theta \] is equal to:

    A) \[\frac{3}{7}\]

    B) \[\frac{8}{25}\]

    C) \[\frac{7}{25}\]

    D) \[\frac{13}{25}\]

    Correct Answer: B

    Solution :

    [b]\[\sin \theta -\cos \theta =\frac{3}{5}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,{{(\sin \theta -\cos \theta )}^{2}}=\frac{9}{25}\]
    \[\Rightarrow \,\,\,\,\,{{\sin }^{2}}\theta +{{\cos }^{2}}\theta -2\sin \theta \cdot \cos \theta =\frac{9}{25}\] \[[{{\sin }^{2}}\theta +{{\cos }^{2}}\theta =1]\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,1-2\sin \theta \cdot \cos \theta =\frac{9}{25}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,2\sin \theta \cdot \cos \theta =\frac{16}{25}\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\sin \theta \cdot \cos \theta =\frac{8}{25}\]


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