SSC Sample Paper SSC CHSL (10+2) Sample Test Paper-10

  • question_answer
    If \[x=r\]sin \[\theta \] cos \[\phi \], y = r sin \[\theta \] sin \[\phi \], z = r cos \[\theta \] then \[{{x}^{2}}+{{y}^{2}}+{{z}^{2}}\] is equal to:

    A) \[{{r}^{2}}\,{{\cos }^{2}}\phi \]        

    B) \[{{r}^{2}}\,{{\sin }^{2}}\theta +{{r}^{2}}{{\cos }^{2}}\phi \]

    C) \[{{r}^{2}}\]               

    D) \[\frac{1}{{{r}^{2}}}\]

    Correct Answer: C

    Solution :

    \[{{x}^{2\text{ }}}+\text{ }{{y}^{2}}+\text{ }{{z}^{2}}\] \[={{r}^{2}}si{{n}^{2}}\theta co{{s}^{2}}\phi +{{r}^{2}}si{{n}^{2}}\theta si{{n}^{2}}\phi +{{r}^{2}}co{{s}^{2}}\theta \] \[={{r}^{2}}si{{n}^{2}}\theta (co{{s}^{2}}\phi +{{r}^{2}}si{{n}^{2}}\phi )+{{r}^{2}}co{{s}^{2}}\theta \] \[={{r}^{2}}si{{n}^{2}}\theta +{{r}^{2}}co{{s}^{2}}\theta \] \[={{r}^{2}}(si{{n}^{2}}\theta +co{{s}^{2}}\theta )={{r}^{2}}\]


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