Chapter 5: Integrals - Section 5.4 - The Fundamental Theorem of Calculus - Exercises 5.4 - Page 287: 39

$\sqrt (1+x^2)$

To find the derivative of an integral, plug in the limits as if you had already integrated and are plugging in the limits to evaluate. Apply chain rule to the variable limit if applicable: $=\sqrt (1+x^2)$