Perimeter is the sum of the lengths of all sides on any given shape. In this case, we know that since the triangle is isosceles, two sides must be the same (in a triangle, two of the same angles will produce two of the same sides opposite of the angles). However, there can not be two 2 inch long sides. Think of this logically; If you had two sides of 2 inches connected to a 5 inch long side, no matter what angle you pull those 2 inch sides down, the maximum it could reach is close to their cumulative sum, or around 4 inches. Since 4 inches isn't long enough to reach above 5 inches, then the only possibility for the side lengths is 5 inches + 5 inches + 2 inches. Thus, the perimeter is 12 inches.
