I have some problems that ask you go verify a linear approximation (easy enough), and then asks you to find the range of values for x which would make it accurate within 0.1. The latter part has me somewhat stumped.

The problem is:

, a=0

which is

and

so

... so that's verified. To get a tolerance of +/- 0.1 you set up the inequality

Here I'm stuck. Can someone point me in the right direction? At this point I'm probably supposed to be doing algebra, but I'm hitting a wall.