; This is how we arrive at Heron's formula for the area
; of any triangle, given side lengths a, b, and c, using the equation
; for the area of a trapezoid with side lengths a, b, c, and d,
; where a and c are the parallel sides (a is the longer parallel side).

; A trapezoid is a quadrilateral with
; exactly two sides that are parallel to each other.

; Equation for the area of a trapezoid:
area=(a+c)/(4*(a-c))*((a+b-c+d)*(a-b-c+d)*(a+b-c-d)*(-a+b+c+d))^.5
copy
replace c with 0 ; make the shorter side length 0
replace d with c ; Heron's formula: