We can use Pythagoras Theorem to prove that a triangle is a right-angle triangle if the square of the two shorter legs add up to be the square of the longest leg.
In this case, we need to prove that 4² + 10² = 12²
<u>Pythagoras Theorem:</u>
Therefore a triangle with side lengths 4 ft, 10ft and 12 ft is not a right angle triangle.