Here is a right angled triangle. The two shorter sides are three and four units long. How many units long is the longest side?
Can you tell without measuring? How?
About 2500 years ago (500 BC) a great Greek, Pythagoras, proved that the square on the longest side of any right angled triangle is equal to the squares on the other two sides added together. We can use his discovery to get our answer. We multiply the length of each sides by itself. We add the answers together. Then we find a number which, multiplied by itself gives us this number.
Here is the answer:
9 + 16 = 25 = 5 x 5
When we multiply a number by itself we “square” it. Any number is the square root of its square. 5 is the square root of 25.
From Pro-English Learning System – International Horizons