Your friend says that since -a is the opposite of a , the opposite of a number is always negative describe and correct the error

He is incorrect due to the fact that the opposite of a negative number is not just another negative number. For instance, the opposite of -2 is actually positive.

hello from mrbilldoesmath!

answer:

the domain is the set { -2, 0, 2, 3}

discussion:

the domain is the set of x values in the ordered pairs (x,y). taking the x, or first component, of each ordered pair gives   -2, 0, 2, 3.

you,

mrb