The longest side of a certain right triangle is 10 units long. Another side is 6 units long. Which of the following represents the length of the triangle's third side?

Explanation

Use the Pythagorean theorem. The longest side of the right triangle measures 10 units. One of the legs measures 6 units.
\(c^{2}=a^{2} + b^{2}\)
\(10^{2}=a^{2} + 6^{2}\)
\(10^{2}-6^{2}=a^{2}\)
\(a=\sqrt{\left(10^{2}-6^{2}\right)}\)