# Given a right triangle ABC with right angle at C, if a is 4 and c is 8, what is b?

$b = 4 \sqrt{3} \approx 6.928$
Assuming that $a$ is the side opposed to the vertex $A$, $b$ is the side opposed to the vertex $B$ and $c$ is the side opposed to the vertex $C$, we have that the hypotenuse is $c = 8$ and $a = 4$ is one of the two legs.
$b = \sqrt{{c}^{2} - {a}^{2}} = \sqrt{{8}^{2} - {4}^{2}} = \sqrt{64 - 16} = \sqrt{48} = \sqrt{16 \cdot 3} = 4 \sqrt{3} \approx 6.928$