Could you please explain number 2 on page 28?
Sure. I assume you’ve already read the solution in the back, which approaches this by plugging in (it is the plugging in chapter drill after all). So I’ll quickly explain why it has to be this way.
Note that you can combine the two given inequalities into one line: 
. Of course, that means we know that the inequality 
, without the 
, is also true! We can simplify that inequality! Just add 
to both sides to end up with all the 
terms on one side:
