Use the Pythagorean theorem:
If c is the hypotenuse of right triangle and a and b are of the legs then:
a² + b² = c².
We have:
a = 4; c= 12
substitute
[tex]4^2+b^2=12^2\\\\16+b^2=144\ \ \ |-16\\\\b^2=128\to b=\sqrt{128}\\\\b=\sqrt{64\cdot2}\\\\b=\sqrt{64}\cdot\sqrt2\\\\\boxed{b=8\sqrt2\approx11.31}[/tex]
