We have P = 3 x a (the formula of the perimeter); 26 = 3 x a ; we obtain a = 26/3;
Then, we have the Pythagorean Theorem in one of two rectangular and congruent triangles :
h² = a² - (a/2)² = a² - a²/4 = 4a²/4 - a²/4 = 3a²/4
It follows that
h = √(3a²/4) = a√3/2 ≈ 0,866*a ≈ 7,5 centimeter.
