― We know that integration is an inverse operation to differentiation. From historical point of view, the concept of integration originated earlier than the concept of differentiation. In fact, the concept of integration owes its origin to the problem of finding area of a plane bounded region. Firstly the definite integral was expressed as a limit of a certain sum expressing the area of some region. The word ‘integration’ has originated from ‘addition’, and the verb ‘to integrate’ means ‘to [...].