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

  • question_answer
    If \[x=r\sin \theta \,cos\phi ,\]  \[y=r\,\sin \theta \,\sin \phi \]and \[z=r\,\cos \theta ,\] then _______.

    A) \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}={{r}^{2}}\]

    B) \[{{x}^{2}}+{{y}^{2}}-{{z}^{2}}={{r}^{2}}\]

    C)  \[{{x}^{2}}-{{y}^{2}}+{{z}^{2}}={{r}^{2}}\]

    D)  \[{{z}^{2}}+{{y}^{2}}-{{x}^{2}}={{r}^{2}}\]

    Correct Answer: A

    Solution :

    \[x=r\]\[x=r\,\sin \theta \,\cos \phi \]                ......(i) \[y=r\,\sin \theta \sin \phi \]                  ?..(ii) \[z=r\cos \theta \]                                 ?..(iii) Squaring and adding (i) and (ii), we get \[{{x}^{2}}+{{y}^{2}}={{r}^{2}}{{\sin }^{2}}\theta \] Squaring (iii) and adding it with (iv), we get \[{{x}^{2}}+{{z}^{2}}+{{y}^{2}}={{r}^{2}}\]


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