10th Class Mathematics Triangles Question Bank Triangles

  • question_answer
    Mason Construction wants to connect two parks on opposite sides of town with a road. Surveyors have laid out a map as shown. The road can be built through the town or around town through point R. The roads intersect at a right angle at point R. The line joining Park A to Park B is parallel to the line joining C and D.            
    (i) What is the distance between the parks through town?
    (ii) What is the distance from Park A to Park B through point R?

    A)  i-9 m               ii-13m

    B)  i-8 m               ii-12.5 m

    C)  i-8.75 m         ii-12 m

    D)  i-9m                ii-14m

    Correct Answer: C

    Solution :

    (i) Since,\[CD||AB\]               [Given] In \[\Delta RCD\] and \[\Delta RBA,\] we have \[\angle BAR=\angle RDC\] \[\angle ABR=\angle RCD\]     [Alternate interior angles] \[\therefore \]  \[\Delta RCD\tilde{\ }\Delta RBA\]         [By AA similarity] \[\Rightarrow \]         \[\frac{BR}{RC}=\frac{AB}{CD}\]                       ...(i) \[\Rightarrow \] \[\frac{7.5}{1.2}=\frac{AB}{1.4}\Rightarrow AB=\frac{7.5\times 1.4}{1.2}=8.75m\] i.e., Distance between the parks through town is\[8.75\text{ }m\]. (ii) In right \[\Delta CRD,\]we have \[{{(CD)}^{2}}={{(CR)}^{2}}+{{(RD)}^{2}}\] \[\Rightarrow \] \[R{{D}^{2}}={{(1.4)}^{2}}-{{(1.2)}^{2}}=0.52\Rightarrow RD=0.72m\] Since \[\Delta RCD\tilde{\ }\Delta RBA\] \[\therefore \] \[\frac{BR}{RC}=\frac{AR}{RD}\,\,\Rightarrow \,\frac{7.5}{1.2}=\frac{AR}{0.72}\] \[\Rightarrow \]  \[AR=\frac{7.5\times 0.72}{1.2}=4.5m\] i.e., Distance from Park A to Park B through point \[R=AR+RB=4.5\,m+7.5m=12\,m\]


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