Triangle ABC is a right triangle. If side AC=5 and side BC=6, What is the measure of side AB?

IF sides AC and BC are the 'legs' of the triangle, then the length of the 3rd side is

√ (5² + 6²) = √ (25 + 36) = √61 = 7.81 (rounded)

IF side BC is the longest side (hypotenuse) of the triangle, then the length of

the 3rd side is

√ (6² - 5²) = √ (36 - 25) = √11 = 3.32 (rounded)