What is the area of a heptagon with a perimeter of 210 yards?

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Since the video you reference deals with regular polygons I will do this problem as a regular heptagon. The formula for area of a regular polygon is (1/2)ap where a stands for the apothem (the perpendicular distance from the center of the polygon to one of its sides) and p stands for the perimeter. To find the apothem, you need to know how to find the tangent of an angle in a triangle. First, divide the heptagon into 7 triangles by drawing a line from the center to each of the vertices. Draw an altitude for one of the triangles- this is your apothem. You have created a right triangle. To find the angle whose vertex is at the center of the heptagon divide 360/14 to get 25 5/7. The bottom of the right triangle is found by dividing the perimeter by 7 and then by 2 : 210/14 = 15 Solve tan(25 5/7) = 15/x x = 22.8 Perimeter = 1/2 x 22.8 x 210 = 2395.88  (answer without rounding in between steps)