Originally Posted by
johnsomeone That's certainly one way to do it - although you'd then need to check that any x value you found that makes f zero is in that part of the domain.
To get you started:
Does f(x) = 0 have a solution on the interval x<-1? (That's the interval $\displaystyle (-\infty, -1)$.)
Solve f(x)=0 on the interval x<-1.
So solve -x=0 on the interval x<-1.
That equation has one solution, x=0, but x=0 isn't in that interval (x<-1, the interval $\displaystyle (-\infty, -1)$ ).
Therefore f(x) = 0 has no solutions on the interval x<-1 ( the interval $\displaystyle (-\infty, -1)$ ).