In this case the answer is very simple.
Step 01:
Data.
hypotenuse=13
side=4
Step 02:
Pythagorean Theorem
h² = a² + b²
13² = 4² + b²
b² = 13² - 4² = 169 - 16 = 153
[tex]b\text{ = }\sqrt[]{153\text{ }}=\text{ }12.37[/tex]The simplest radical form is.
[tex]b\text{ = }\sqrt[]{9\cdot17}[/tex][tex]b\text{ = 3}\sqrt[]{17}[/tex]The solution is:
[tex]b\text{ = 3 }\sqrt[]{17}[/tex]