The definition of definite integral Who can explain exactly what is definite integral Not too much

The definition of definite integral Who can explain exactly what is definite integral Not too much

The definition of definite integral: let the function of one variable y = f (x), which is defined in the interval (a, b). Divide the interval (a, b) into n small areas (a, x0) (x0, x1) (x1, x2). (Xi, b). Let △ xi = xi-x (i-1), take any point on the curve in the interval △ Xi as f (ξ I), make the sum formula: if λ is these small areas