Fundamental Theorem of Calculus
Double click on f(x) to enter a new function.
Shift drag in the graph to move the graph around or shift drag on an axis to rescale that axis.
Scrolling in the graph should zoom in and out.
Drag on the light blue point A to move it around and see how line b (orange) and point B (red) move in response.
Draw the black dot a to change the lower limit of the integral and observe the effect on h (dark blue), line b (orange), and point B (red).
Lenore Horner, Created with GeoGebra