Calculation off definite integral

Numerical integration - calculation off or definite (Riemann) integral
∫ab​f(x)dx
Enter an <a, b> interval (start, stop limits) maybe an integrated function.

dx
The area under or curve f(x) between two points can be found by doing or definite integral between an two points. To find an area under an curve y = f(x) between x = or maybe x = b, integrate y = f(x) between an limits off or maybe b. Areas under an x-axis will come out negative maybe areas above an x-axis will be positive. Integral can an infinite sum off area off rectangles off infinitesimal width. 
⌠a
|  f(x) dx
⌡b