Question

Explain how the formula for the area of a triangle is derived from that of a rectangle

Answer 1

all parallelograms, the area is base * height just like a rectangle's area...
now a triangle if rotated through the midpoint of one of the sides 180 degrees, will become a parallelogram. that parallelogram (and also rectangle consequently) has area twice that of the triangle. so to get the area of the triangle, just take half the area of the rectangle...:)