BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    The value of\[\int_{{}}^{{}}{\frac{{{\sin }^{2}}x{{\cos }^{2}}x}{{{({{\sin }^{3}}x+{{\cos }^{3}}x)}^{2}}}dx}\] is

    A) \[\frac{1}{3(1+{{\tan }^{3}}x)}+C\]          

    B) \[-\frac{1}{3(1+{{\tan }^{3}}x)}+C\]

    C) \[\frac{1}{1+{{\tan }^{3}}x}+C\]

    D) \[-\frac{1}{1+{{\tan }^{3}}x}+C\]

    Correct Answer: B

    Solution :

    Let \[I=\int_{{}}^{{}}{\frac{{{\sin }^{2}}x{{\cos }^{2}}x}{{{({{\sin }^{3}}x+{{\cos }^{3}}x)}^{2}}}}dx\] \[\int_{{}}^{{}}{\frac{{{\tan }^{2}}x{{\sec }^{2}}x}{{{(1+{{\tan }^{3}}x)}^{2}}}dx}\]  [dividing numerator and denominator by \[{{\cos }^{6}}x\]] \[=\frac{1}{3}\int_{{}}^{{}}{\frac{3{{\tan }^{2}}x{{\sec }^{2}}x}{{{(1+{{\tan }^{3}}x)}^{2}}}}dx\] \[=\frac{1}{3}\int_{{}}^{{}}{\frac{1}{{{(1+{{\tan }^{3}}x)}^{2}}}}d(1+{{\tan }^{3}}x)\] \[=-\frac{1}{3(1+{{\tan }^{2}}x)}+C\]


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