® We have defined

® We have defined a f x dx as the area of the region bounded by the curve y = f ( x ), a ≤ x ≤ b , the x -axis and the ordinates x = a and x = b . Let x be a INTEGRALS given point in [ a , b ]. Then a f x dx represents the Area function A ( x ). This concept of area function leads to the Fundamental Theorems of Integral Calculus.