The pythagoras theorem is the rule used to work out the length of side of a right angle triangle with one length mising and two known lengths of side. The rule states that a2 = b2+c2.
"a" represents the hypotenuse and "b" and "c" represent the other sides. If the hypotenuse is given in the quiestion the equation must be rearranged. The most common mistakes are forgetting to rearragne the equations and forgetting to move the square over to the other side.