Question 325141
Sides of an equilateral triangle are all of equal length. In this case, 5 cm
{{{AreaOfTriangle = (bh)/2}}}
So, since all sides are 5, we need to find h.
Draw an equaliateral triangle with b across the bottom.
Drop a perpendicular line from the 'peak' down to the base.
That will result in two smaller right triangles. Each of those triangles has sides of length 2.5, 5 and h.
Use pathagorean theorem to solve for h
{{{h^2 = 5^2 + (2.5)^2}}} 
You do the math.
Once you have h, then plug that value into the Area formula above.

Let me know if you can't solve this now