Pythagoras theorem states that the square of the hypotenuse is equal to the sum of the squares of the other two sides.
[tex]a^2+b^2=c^2[/tex]
[tex]5^2+12^2=13^2[/tex]
[tex]25+144=169[/tex]
[tex]169=169[/tex]
Hence, this triangle is right-angled.
