Explanation:
Thomas draws a triangle with side lengths of 5 centimeters and 12 centimeters and one angle of 90.
If one of the angle is 90 degrees, it would mean that he has drawn a right angle triangle.
Hypotenuse is the longest side of the triangle. We can find it using Pythagoras theorem as follows:

The longest side is 13 cm.
If we keep the longest side the same and if two sides i.e. 5 cm and 12 cm are replaced, a new triangle can form.