Whats is the area of an equilateral triangle, with sides equaling 15 cm?

1 Answer
Dec 1, 2015

#(225sqrt3)/4# #"cm"^2#

Explanation:

jwilson.coe.uga.edu

We can see that if we split an equilateral triangle in half, we are left with two congruent equilateral triangles. Thus, one of the legs of the triangle is #1/2s#, and the hypotenuse is #s#. We can use the Pythagorean Theorem or the properties of #30˚-60˚-90˚# triangles to determine that the height of the triangle is #sqrt3/2s#.

If we want to determine the area of the entire triangle, we know that #A=1/2bh#. We also know that the base is #s# and the height is #sqrt3/2s#, so we can plug those in to the area equation to see the following for an equilateral triangle:

#A=1/2bh=>1/2(s)(sqrt3/2s)=(s^2sqrt3)/4#

Since in your case #s=15#, the area of the triangle equals:
#(15^2sqrt3)/4=(225sqrt3)/4# #"cm"^2#