# Triangular conundrum

Place any three numbers on the vertices of a triangle:

         5
/ \
/   \
/     \
8-------4


Calculate their differences, going one way:

         5
/ \
-3  /   \ -1
/     \
8-------4
4


Place another number inside the triangle:

         5
/ \
-3  /   \ -1
/ 15  \
8-------4
4


Add the centre number to a vertex, and multiply the total by the opposite edge. Do this for each vertex. Add them together.

$$(15+5)\times4=80$$
$$(15+8)\times-1=-23$$
$$(15+4)\times-3=-57$$

$$80-23-57=0$$

You got $$0$$. Why?

• Because math is cool. Apr 7 '20 at 11:41

• Should be $(d+c)(a-b)$ et cetera Apr 7 '20 at 11:45