Answer :

the height of triangle is 6cm
then base length is found by pythagoras theorem
[tex] a^{2}= ( \frac{a}{2} )^{2}+ h^{2} [/tex]
[tex] \frac{3a^2}{4}=36 [/tex]
[tex] a^{2}=48 [/tex]
[tex]a= \sqrt{48} [/tex]
The area of the triangle
[tex]= \frac{1}{2}ah =3 \sqrt{48}=20.7846 cm^2 [/tex]


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Height of equilateral triangle is  √3/2 X a, where 'a' is the side of the equilateral triangle. So √3/2 x a = 6.  
Hence a = 12/√3.
   Area of an equilateral triangle is 1/2  base x height
ie   1/2 x 12 ÷ √3  x 6  =  36 ÷√3
  =  12√3.

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