From this diagram the voltage drop actually you have seen it is Ircosθ+Ixlsinθ when series capacitor was not there right, so it is equation 1. Similarly this all the nomenclature is given right.
या आकृतीवरून मालिका कॅपॅसिटर नसताना विद्युत दाबात झालेली घट आपण बघितली ती तर हे समीकरण 1 .