Rectangles Squares Triangles Parallelograms Rhombuses Trapezoids Circles and sectors Other polygons Quiz on Area Rectangle Area The area A of any rectangle is equal to the product of the length l and the width w. Formula: A = lw Back to Top  Square Area Theorem The area A of any square is equal to the square of the length s of a side. Formula: A = s2 Back to Top  Triangle Area Theorem The area A of any triangle is equal to one-half the product of any base b and corresponding height h. Formula: A = .5bh Back to Top  Parallelogram Area Theorem The area A of any parallelogram is equal to the product of any base b and the corresponding height h. Formula: A = bh Back to Top  Rhombus Area Theorem The area A of any rhombus is equal to one-half the product of the lengths d1 and d2 of its diagonals. Formula: A = .5d1d2 Back to Top  Trapezoid Area Theorem The area A of any trapezoid is equal to one-half the product of the height h and the sum of the bases, b1 and b2. Formula: A = .5h(b1 + b2) Back to Top  Circle Area Postulate The area A of any circle is equal to the product of PI and the square of the radius r. Formula: A = (PI)r2 Sector Area Theorem The area A of any sector with an arc that has degree measure n and with radius r is equal to the product of the arc's measure divided by 360 multiplied by PI times the square of the radius. Formula: A = (n/360)((PI)r2) Back to Top  Regular polygons are any polygons that are equilateral and equiangular. Regular Polygon Area Theorem The area A of any regular polygon with perimeter P and apothem of measure a is equal to one-half the product of the perimeter and the apothem. Formula: A = .5aP Back to Top