Using the Pythagorean theorem:
[tex] {c}^{2} = {a}^{2} + {b}^{2} [/tex]
And expressing hypotenuse.
[tex]c = \sqrt{ {a}^{2} + {b}^{2} } [/tex]
Now...
1.
[tex]c = \sqrt{ {12}^{2} + {16}^{2} } = 20 [/tex]
2.
[tex]c = \sqrt{ {5}^{2} + {12}^{2} } = 13[/tex]
3.
[tex]c = \sqrt{ {15}^{2} + {8}^{2} } =17 [/tex]
