In the book (page 31) two's complement of x is said to be calculated by (2^n)-x. It then goes on to say that to calculate -2 you perform the following operation: (2^4)-2. However, why if x=-2 in this case is it (2^4)-2 and not (2^4)-(-2)? Also, to calculate two's complement where x=2, one would perform the operation: (2^4)-(-2) in order to yield the result 0010.
I think Andreas is right to be confused, because the text fails to clearly distinguish between "the 2's complement of the number x" and "the 2's complement representation of the number x".
An additional sentence in the text is needed at the beginning of the "For example ..." paragraph. This sentence might read, "The 2's complement representation of a negative number x is the 2's complement of it's absolute value, |x|."