JEE Main & Advanced Mathematics Straight Line Question Bank Self Evaluation Test - Straight Lines & Pair Striaght Lines

  • question_answer
    If the angle between the two lines represented by \[2{{x}^{2}}+5xy+3{{y}^{2}}+6x+7y+4=0\] is \[{{\tan }^{-1}}m.\] then m is equal to:

    A) \[\frac{1}{5}\]

    B) 1

    C) \[\frac{7}{5}\]

    D) 7

    Correct Answer: A

    Solution :

    [a] We have, \[2{{x}^{2}}+5xy+3{{y}^{2}}+6x+7y+4=0\] comparing this eq. with \[a{{x}^{2}}+b{{y}^{2}}+2hxy+2gx+2fy+c=0.\] we get \[a=2,b=3,h=\frac{5}{2}\] \[\therefore \tan \theta =\frac{2\sqrt{{{h}^{2}}-ab}}{a+b}=\frac{2\sqrt{\frac{25}{4}-2\times 3}}{2+3}\] \[=\frac{2\sqrt{\frac{1}{4}}}{5}=\frac{2\times \frac{1}{2}}{5}=\frac{1}{5}\tan \theta =\frac{1}{5}\Rightarrow m=\frac{1}{5}\]


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