4.  Complete the hexagonal and star shaped Rangolies [see Fig. (i) and (ii)] by filling them with as many equilateral triangles of side \small 1 cm as you can. Count the number of triangles in each case. Which has more triangles?

                                

Answers (1)

For finding the number of triangles we need to find the area of the figure.

Consider the hexagonal structure :

                      Area of hexagon  =   6  \times   Area of 1 equilateral 

Thus area of the equilateral triangle :           

           =\ \frac{\sqrt{3}}{4}\times a^2

or        =\ \frac{\sqrt{3}}{4}\times 5^2

or        =\ \frac{25\sqrt{3}}{4}\ cm^2

So, the area of the hexagon is  : 

       =\6\times \frac{25\sqrt{3}}{4}\ =\ \frac{75\sqrt{3}}{2}\ cm^2

And the area of an equilateral triangle having 1cm as its side is :

       =\ \frac{\sqrt{3}}{4}\times 1^2

or    =\ \frac{\sqrt{3}}{4}\ cm^2

Hence a number of equilateral triangles that can be filled in hexagon are :     

    =\ \frac{\frac{75\sqrt{3}}{2}}{\frac{\sqrt{3}}{4}}\ =\ 150

Similarly for star-shaped rangoli :

 Area :             

   =\12\times \frac{\sqrt{3}}{4}\times 5^2 \ =\ 75\sqrt{3}\ cm^2

Thus the number of equilateral triangles are : 

      =\ \frac{75\sqrt{3}}{\frac{\sqrt{3}}{4}}\ =\ 300

Hence star-shaped rangoli has more equilateral triangles.

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