The lateral side of an isosceles triangle is 29cm and its height is 21cm. What is the base of the triangle?

Let the base of the triangle be equal to a, the height equal to n = 21 cm, the side side b = 29 cm. Consider a triangle composed of half of the base (a / 2), height h, and the side side b.

(a / 2) ^ 2 = 29 ^ 2 – 21 ^ 2 = (29 + 21) * (29 – 21) = 50 * 8 = 400 cm. Whence (a / 2) = √ 400 = 20 cm. Where a = 2 * 20 = 40 cm.