Sign In
A=21h(b1+b2)
Consider a trapezoid with bases b1 and b2 and height h.
Drawing a diagonal divides the trapezoid into two triangles. Therefore, the area of the trapezoid can be written as the sum of the areas of the triangles.
Take b2 as the base of the upper triangle and draw the corresponding altitude from the opposite vertex.
A1=21b1h, A2=21b2h
Factor out 21h