Question

The perimeter of an equilateral triangle is 30 cm .find its area

Answer 1

if the perimeter of an equilateral triangle is 30 cm.Then its side will be 10 cm as in an equilateral triangle all sides are equal.
now if side is 10 cm then it's area would be =
a^2 √3/4. hence the area would be 43.30

Answer 2

aloha!

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we know that perimeter of triangle is sum of three sides.
and it is an equilateral triangle so all sides would be same let them be x cm

so,
x + x + x = 30
3 x = 30
x = 10 

now we know area of equilateral triangle is $\frac{ \sqrt{3} }{4} x^{2}$

now the side is 10 cm,

then

 $\frac{ \sqrt{3} }{4} 10^{2}$  
area= 43.3 $cm^{2}$ or 25√3  $cm^{2}$ 


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hope it helps :)