The common difference can be determined by subtracting the first term with the second term, second term with the third term, and so forth.
In this case we have:
[tex]1-(-1)=1+1=2[/tex][tex]-1-(-3)=-1+3=2[/tex][tex]-3-(-5)=-3+5=2[/tex]In this way we can determine that the common difference of the sequence is 2, so the statement is true.