Let us look at a problem now. Triangle PQR is given to have sides of length 7 cm, 24 cm and 25 cm respectively. We need to find out if it is a right triangle?
By Pythagoras Theorem, In a right triangle, the sum of the squares of the two shorter sides will be equal to the square of the longer side. Let us see if this is true for this triangle.
In this case sides PQ and QR are shorter than side PR. Hence we compute PQ squared plus QR squared
which gives 24 squared plus 7 squared
which gives 576 plus 49 which gives 625
The longest side PR when squared gives 25 squared which is 625.
Thus we see that PQ squared plus QR squared is indeed equal to PR squared. Hence by the converse of the Pythagoras theorem, PQR is a right triangle, with the 90 degree angle at vertex Q.