JEE Main & Advanced Mathematics Three Dimensional Geometry Question Bank Self Evaluation Test - Three Dimensional Geometry

  • question_answer
    What is the angle between the lines\[\frac{x-2}{1}=\frac{y+1}{-2}\] and \[\frac{x-1}{1}=\frac{2y+3}{3}=\frac{z+5}{2}?\]

    A) \[\frac{\pi }{2}\]

    B) \[\frac{\pi }{3}\]

    C) \[\frac{\pi }{6}\]

    D) None of the above

    Correct Answer: A

    Solution :

    [a] The given lines are:- \[\frac{x-2}{1}=\frac{y-(-1)}{-2}=\frac{z-(-2)}{1}\] and \[\frac{x-1}{1}=\frac{y-\left( -\frac{3}{2} \right)}{\frac{3}{2}}=\frac{z-(-5)}{2}\] Dr?s of 1st line are:- \[{{a}_{1}}=1,{{b}_{1}}=-2,{{c}_{1}}=1\] Dr?s of IInd line are:- \[{{a}_{2}}=2,{{b}_{2}}=3,{{c}_{2}}=4\] Let \['\theta '\] be the angle b/w two lines, then. \[\cos \theta =\frac{\left| {{a}_{1}}{{a}_{2}}+{{b}_{1}}{{b}_{2}}+{{c}_{1}}{{c}_{2}} \right|}{\sqrt{a_{1}^{2}+b_{1}^{2}+c_{1}^{2}}.\sqrt{a_{2}^{2}+b_{2}^{2}+c_{2}^{2}}}\] \[\cos \theta =0\] \[\Rightarrow \theta =\frac{\pi }{2}\]


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