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Pythagoras Theorem

The Pythagoras Theorem allows us to find the length of the third side on a right angle triangle if we know the other two lengths.

Don’t forget:

It only works on right angled triangles.

You need to know at least two other lengths.

The formal definition is: In a right angled triangle the sum of the square of the hypotenuse is equal to the sum of the squares of the other two sides.

Algebraically a² + b² = c²

('a' squared plus 'b' squared equals 'c' squared)

c is always the hypotenuse.

Therefore 3² + 4² = 5^{2

(three squared plus four squared equals five squared)}

Which goes to 9 + 16 = 25

This can be used to find the length of an unknown side

right angled triangle

a² + b² = c²

5² + 12² = c²

25 + 144 = 169

c² = 169

c = √169 (square root of 169)

c = 13

Check that you understand what these words mean in this document
Right angled triangle: the geometrical shape of three sides whose one angle is 90 degrees.
Hypotenuse: the side opposite the right angle.

For further information visit:
Proof of Pythagoras Theorem