Let's use Pythagorean theorem. [tex]a^{2}+b^{2}=c^{2}[/tex] where [tex]c[/tex] is the hypotenuse.
So if we set it up:
[tex]7^{2}+b^{2}=13^{2}[/tex]
now we simplify:
[tex]49+b^{2}=169[/tex]
and get [tex]b^{2}[/tex] by itself:
[tex]b^{2}=120[/tex]
Now to get [tex]b[/tex] by itself, we need to take the square root of both sides:
[tex]b=\sqrt{120}[/tex]
And that's your answer!
