Pythagoras’ theorem states that for all right-angled triangles, **‘The square on the** hypotenuse **is equal to the sum of the squares on the other two sides’**. The hypotenuse is the longest side and it’s always opposite the right angle.

In this triangle **a ^{2} = b^{2} + c^{2} **and angle

**A**is a right angle.

Pythagoras’ theorem only works for right-angled triangles, so you can use it to test whether a triangle has a right angle or not.

In the triangle above, if **a ^{2} < b^{2} + c^{2} **the angle

**A**is acute.

In the triangle above, if **a ^{2} > b^{2} + c^{2 }**the angle

**A**is obtuse.

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