## Elementary Algebra

$c = 2\sqrt 10$
Through Pythagorean Theorem, we obtain: $2^2 + 6^2 = c^2$, which simplifies to $4+36 = c^2$ To solve for c, take the square root of both sides: $c = \sqrt 40 = \sqrt (4 \times 10) = 2\sqrt 10$