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

  • question_answer
    If \[x=r\,\sin \theta .\cos \phi ,\] \[y=r\sin \theta .\sin \phi \]and \[z=r\,\cos \theta ,\]then the value of \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}\]is independent of:

    A) \[r,\theta \]

    B) \[r,\phi \]

    C) \[\theta ,\phi \]

    D) \[r\]

    Correct Answer: C

    Solution :

    [c]\[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}={{r}^{2}}{{\sin }^{2}}\theta {{\cos }^{2}}\phi +{{r}^{2}}{{\sin }^{2}}\theta \cdot {{\sin }^{2}}\phi +{{r}^{2}}{{\cos }^{2}}\theta \]
    \[={{r}^{2}}{{\sin }^{2}}\theta ({{\cos }^{2}}\phi +{{\sin }^{2}}\phi )+{{r}^{2}}{{\cos }^{2}}\theta \]
    \[={{r}^{2}}({{\sin }^{2}}\theta +{{\cos }^{2}}\theta )={{r}^{2}},\] which is independent of \[\theta ,\phi \].


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