10th Class Mathematics Introduction to Trigonometry Question Bank Trigonometry

  • question_answer
    If \[x=m\text{ }sin\theta \] and \[y=n\text{ }cos\theta \], What is the value of \[{{n}^{2}}{{x}^{2}}+{{m}^{2}}{{y}^{2}}\]?

    A)  \[mn\]                          

    B)  \[m{{n}^{2}}\]

    C)  \[1\]                            

    D)  \[{{m}^{2}}{{n}^{2}}\]

    Correct Answer: D

    Solution :

    (d):       \[x=m\sin \theta \]          \[\Rightarrow \]   \[{{x}^{2}}={{m}^{2}}{{\sin }^{2}}\theta \] \[y=n\cos \theta \] \[\Rightarrow \]   \[{{y}^{2}}={{n}^{2}}{{\cos }^{2}}\theta \]             \[{{n}^{2}}{{x}^{2}}={{m}^{2}}{{n}^{2}}{{\sin }^{2}}\theta \]__________(1)             \[{{m}^{2}}{{y}^{2}}={{m}^{2}}{{y}^{2}}{{\cos }^{2}}\theta \]_________(2) \[\therefore \]      \[{{n}^{2}}{{x}^{2}}+{{m}^{2}}{{y}^{2}}={{m}^{2}}{{n}^{2}}\]


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