The formula for a trapezoid, if you understand the angles don't matter, is very easy to derive visually. Like in a cut and paste common core number sense kind of way. If it's symmetrical you fit the left triangle into the space above the right triangle and get a rectangle that is the length of the short side plus another rectangle that's half the difference in the lengths. The area of this trapezoid is the same as any other one with the same bases, so it doesn't really have to be algebra at all. It's like starter geometry. I don't remember the formulas from school and just thought about the idea and then double checked with Google that I know what a trapezoid was. It looks harder than it is, until you draw it.
