Answer
$c(b-a)$
Work Step by Step
RIEMANN SUM states that:
$\Sigma_{k=1}^n f(c_k) \triangle x=\Sigma_{k=1}^n \dfrac{c(b-a)}{n}$
or, $\Sigma_{k=1}^n \dfrac{c(b-a)}{n}=c(b-a)$
where $\triangle x=\dfrac{b-a}{n}; c_k=a+\dfrac{k(b-a)}{n}$
Now, $\lim\limits_{n \to \infty} \Sigma_{k=1}^n f(c_k) \triangle x=\lim\limits_{n \to \infty}c(b-a)$
Hence, $\int_a^{b} cdx=c(b-a)$
