Isosceles right triangles are half squares, and if the length of one side is 6cm, that is the length of the other side since both segments are equal. Take the formula to find the area of a square (base times height), apply the side measurement of the triangle (6cm) and divide it in half to find the area of half of it (therefore, finding the area of the isosceles triangle.)
(6x6) / 2 6x6 = 36 36 / 2 = 18
The area of the isosceles triangle is 18 square centimeters.
