If it is isosceles, than the legs are the same. We will call them X. The formula for the area of a triangle is 1/2 (base * height). But the base and the height are both X. So the area (18) is equal to 1/2 (x * x), or 1/2(x^2). This means that 36 = x^2. Thus, the length of each side is 6 inches. You can check this work by plugging those into the formula for area. You will find that it equals 18.
