Definite integrals are only different in that they are NOT ended with C, but rather are evaluated at certain values. The whole idea of definite integrals is to measure quantities, what is represented by the final value.
\(ex. a\)
\(\int_{1}^{3}\,(x)\,dx = [\dfrac{x^{2}}{2}]_{1}^{3} = [\dfrac{(3)^{2}}{2}] - [\dfrac{(1)^{2}}{2}] = \dfrac{8}{2} = 4 \)
