10th Class Mathematics Mensuration Question Bank Mensuration

  • question_answer
    A wire in the shape of an equilateral triangle encloses an area , s1 sq. cm. If the same wire is bent to form circle, the area of the circle will be

    A)  \[\frac{\pi {{s}^{2}}}{9}\]            

    B)         \[\frac{3{{s}^{2}}}{\pi }\]

    C)  \[\frac{3s}{\pi }\]                           

    D)         \[\frac{3\sqrt{3s}}{\pi }\]  

    Correct Answer: D

    Solution :

     If the side of the triangle be a cm, then \[S=\frac{{{a}^{2}}\sqrt{3}}{4}\]                 or            \[{{a}^{2}}=\frac{4S}{\sqrt{3}}\] and the perimeter of the triangle \[=3a\] \[\therefore \] Circumference of the circle \[=3a\] \[\therefore \] If r be the radius of the circle, \[2\pi \,\,r=3a\] \[\therefore \]  \[r=\frac{3a}{2\pi }\] \[\therefore \]Area of the circle \[=\pi \,{{r}^{2}}\]                                 \[=\pi \times \frac{9{{a}^{2}}}{4{{\pi }^{2}}}=\frac{9}{4\pi }\times \frac{4S}{\sqrt{3}}\]                                 \[=\frac{3\sqrt{3}\,S}{\pi }\]


You need to login to perform this action.
You will be redirected in 3 sec spinner