Finding the Area of a Trapezoid in the Coordinate Plane Using the Box Method. What is the area of the trapezoid? Draw the box around the trapezoid B Area of rectangle: and label triangles 1, 2, and 3. y 20 18 16 14 12 = (12)(10) = Area of triangle 1: (3)(6)(12) = Area of triangle 2: (2)(4)( = Area of triangle 3: (2)(4)(8) = == Area of trapezoid: 120-36-8-16= 10 8 6 4 2 X 2 4 6 8 10 12 14 16 18 20 units Finding an Unknown Side Length The area of a trapezoid is 86.86 square inches. The height is 17.2 inches, and one base is 6 inches. What is the length of the other base? 1 (b + b) = A (17.2) (6 + x) = 17.2(6+x) = = 173.72