We now will constructfour rectanglesthat will serveas the basisfor our approximationof the area.The
subintervalswill serveas the widthof the rectangles.We will take the lengthof eachrectangleto be the
maximumvalueof the functionin the subinterval.Hencewe get the followingfigure:
If we call the rectanglesR1–R4,from left to right,then we havethe areas