The pythagorean (pi-THA-gor-in) theorem is a formula which explains the relationship between sides of a right triangle (a triangle w/ one 90 degree angle)

Formula:

${\displaystyle a^{2}+b^{2}=c^{2}}$ where a and b are the legs and c is the hypoteneuse.

There is also a thing called a Pythagorean Triple, where in ${\displaystyle a^{2}+b^{2}=c^{2}}$ a and b are equal to c.

Such an example is with ${\displaystyle 3^{2}+4^{2}=c^{2}}$ Where ${\displaystyle 3^{2}=9}$ and ${\displaystyle 4^{2}=16,16+9=5^{2}}$ which is 25