Find the Hypotenuse AC in Right Triangle with Legs 6 and 18

To solve this problem, we'll apply the Pythagorean theorem to find the hypotenuse $AC$ of the right triangle $\triangle ABC$.

According to the Pythagorean theorem:
$a^2 + b^2 = c^2$

Here, $a = AB = 6$ and $b = BC = 18$ are the legs of the triangle, and $c = AC$ is the hypotenuse.

Substitute these values into the formula:
$6^2 + 18^2 = AC^2$

Calculate each square:
$6^2 = 36$
$18^2 = 324$

Add the squares of the legs:
$36 + 324 = 360$

Thus,
$AC^2 = 360$
Taking the square root of both sides gives:
$AC = \sqrt{360}$

Therefore, the length of $AC$ is $\sqrt{360}$.