A rate of change is the slope of a curve at a point... which is the same as the slope of the line tangent to the curve at that point.

So you could draw a tangent to the curve at the point and measure its slope using .

You could also choose another point very close to 2, say 2.001, and work out the slope of the line that would cross the two points, using . This will give you a good approximation.

Using calculus, if a function , its derivative (rate of change at any point) is given by . Substitute into the derivative and this will be the slope of the curve at that point.