Helen's formula s △ = √ (p (p-a) (p-b) (p-c)) p = (a+b+c)/2abc is the length of each side of a triangle. Helen's theorem is that if you haven't learned formulas in junior high school, it's useless to want them as a junior high school student. Maybe you're out of class and don't give points. Besides, you just remember the formula and can't push it.