I dont have the same book, so I dont know the exact amplifier you are referring to, but if you go and set up the small signal model of the FETs in the circuit, and then do the analysis like that, finding the input current and voltage, as well as the output current and voltage will be all the information you need, as you can just use the relationship V/I = R to find both your input and output resistance.
The book I have is Sedra/Smith and is called "Microelectronic Circuits"
Single-Stage Discrete MOS amplifiers are covered in chapter 4 secion 4.7 and there is a pretty full description of how to analyze these circuits. If you dont know what the small signal model is, you should probably look that up if you are going to need to know how to analyze these circuits more, but if not, I can try to quickly explain it to you...