SSC Quantitative Aptitude Trigonometry Question Bank Trigonometry (I)

  • question_answer
    If \[x=\cos ec\,\theta -\sin \theta \] and \[y=\sec \theta -\cos \theta ,\] then the value of \[{{z}^{2}}{{y}^{2}}({{x}^{2}}+{{y}^{2}}+3)\] is

    A) 0

    B) 1

    C) 2

    D) 3

    Correct Answer: B

    Solution :

    [b] \[{{x}^{2}}+{{y}^{2}}+3={{(cosec\theta -sin\theta )}^{2}}+{{(sec\theta -cos\theta )}^{2}}+3\]            \[=\text{cose}{{\text{c}}^{2}}\theta +{{\sec }^{2}}\theta -3+3\] \[=\frac{1}{{{\sin }^{2}}\theta {{\cos }^{2}}\theta }\] \[{{x}^{2}}{{y}^{2}}={{(cosec\theta -sin\theta )}^{2}}{{(sec\theta -cos\theta )}^{2}}\] \[={{\left( \frac{1}{\sin \theta }-\sin \theta  \right)}^{2}}{{\left( \frac{1}{\cos \theta }-\cos \theta  \right)}^{2}}\] \[={{\left( \frac{1-{{\sin }^{2}}\theta }{\sin \theta }.\frac{1-{{\cos }^{2}}\theta }{\cos \theta } \right)}^{2}}\] \[={{\left( \frac{{{\cos }^{2}}\theta .{{\sin }^{2}}\theta }{\sin \theta \cos \theta } \right)}^{2}}\] \[={{\cos }^{2}}\theta {{\sin }^{2}}\theta \] \[\therefore \]      \[{{x}^{2}}{{y}^{2}}({{x}^{2}}+{{y}^{2}}+3)\] \[=\frac{1}{{{\sin }^{2}}\theta {{\cos }^{2}}\theta }\cdot {{\cos }^{2}}\theta {{\sin }^{2}}\theta =1\]


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