SSC Quantitative Aptitude Trigonometry Question Bank Trigonometry (II)

  • question_answer
    If\[0\le \theta \le \frac{\pi }{2},\]\[2y\cos \theta =x\]and \[2\,x\sec \theta -y\,\text{cosec}\,\theta =3,\] then the value of \[{{x}^{2}}+4{{y}^{2}}\] is

    A) 1

    B) 2

    C) 3

    D) 4

    Correct Answer: D

    Solution :

    [d] Given, \[2y\cos \theta =x\sin \theta \]               ...(i) \[\Rightarrow \]   \[2y\cdot \frac{1}{\sec \theta }=\frac{x}{\text{cosec}\theta }\] \[\Rightarrow \]   \[x\sec \theta -2y\cos ec\theta =0\] and \[2x\sec \theta -y\,\text{cosec}\theta =3\]        ...(iii) On solving Eqs. (i) and (ii), we get \[y=\sin \theta \] From Eq. (i), we get \[x=2\cos \theta \] \[\therefore \]      \[{{x}^{2}}+4{{y}^{2}}={{(2cos\theta )}^{2}}+4\,{{(sin\theta )}^{2}}\] \[=4\,(co{{s}^{2}}\theta +si{{n}^{2}}\theta )=4\]


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