The flag is an isosceles triangle. A flag is an isosceles triangle. The height of the flag is x. The angle opposite to x is 36 degrees. The side above the angle is 5 feet. The bottom side of the flag measures 5 feet because the triangle is . Because , the trigonometric triangle formula is used to calculate that the area is One-half(5)(5)sin(36°) ≈ 7.35 square feet. Recalling that this triangle is isosceles, we can write the area equation to solve for x. = One-half(x)(5)sin(). Solving for x and adding this value to the length of the other sides, the perimeter ≈ (rounded to the nearest tenth).