My question is that why is their a need for both upper and lower while calculating Definite Integrals. The question arose when i thought of Definite integration as something related to Differentiation. Or is it that only Indefinite Integration is directly related to differentiation. In differentiation, we get the slope or rate of change. So if i differentiate s(displacement) w.r.t. t(time), i get ds/dt = v(Velocity). By putting just one value of t, i get a value of velocity at that instant. But to get back that one value of s(displacement), why do we need two values of t(time)?