Well, the change in f is the value of f at the upper point here, which is x0+delta x, and minus its value at the lower point P, which is f of x0, divided by delta x.
F Coastal freshwater lagoons; includes freshwater delta lagoons.
沿海淡水泻湖，包括淡水三角洲的泻湖。
3
What the imagery shows is a large fighter, approaching the size of an F-111, with a canard delta configuration and pair of outward canted all moving vertical tails.