JEE Main & Advanced Mathematics Straight Line Question Bank Angle between two straight lines, Bisector of angle between two lines

  • question_answer
    Angle between the lines \[2x-y-15=0\] and \[3x+y+4=0\]is                                         [RPET 2003]

    A)            \[{{90}^{o}}\]                      

    B)            \[{{45}^{o}}\]

    C)            \[{{180}^{o}}\]                    

    D)            \[{{60}^{o}}\]

    Correct Answer: A

    Solution :

    Lines are \[p=\left| \frac{-k}{\sqrt{{{\sec }^{2}}\alpha +\text{cose}{{\text{c}}^{2}}\alpha }} \right|\]                      .....(i) and         \[3x+y+4=0\]           ......(ii) Here,  \[{{m}_{1}}=2,\,{{m}_{2}}=-\,3\] If angle between them is \[\theta \], then                    \[\tan \theta =\left| \frac{{{m}_{1}}-{{m}_{2}}}{1+{{m}_{1}}{{m}_{2}}} \right|\] \[=\left| \frac{2+3}{1-6} \right|=\left| \frac{5}{-5} \right|\]= 1                    \[\tan \theta =\tan \frac{\pi }{4}\] Þ \[\theta =\frac{\pi }{4}=45{}^\circ .\]


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