Chapter 13.2, Problem 70E

To determine

To prove that second part of the Fundamental Theorem of Calculus for Vector-Valued Functions that if $r\left(t\right)$ is continuous on an open interval I, and a be in I, then $\frac{d}{dt}{\displaystyle {\int }_a^{t}r\left(s\right)ds}=r\left(t\right)$ by using the Fundamental Theorem of Calculus II from single-variable calculus.