Let us look at this right triangle ABC. It is right angled at B and sides AB and BC are of length 3 and 4 centimeters each. What is the length of side AC?
By Pythagoras Theorem, we know that AB squared plus BC squared equals AC squared.
AB squared plus BC squared equals 3 squared plus 4 squared which equals 9 plus 16 which sums up to 25.
Now AC squared is 25. Which number when squared gives 25? The answer is 5. Hence AC is of length 5 centimeters as well.