Question

in problem set2, the first question says by using(2). any one knows what does that "(2)" refer to? Thanks

Answer 1

If you look back through the text there are formulas that have (1) or (2) or some other number off to the side. (2) refers to the formula or equation that has that number next to it.

Answer 2

The corresponding formula is the linear approximation definition : \[\Delta y / \Delta x \approx f'(x0)\]
The other formula are the approximation of the basic function.