Let #f(a)=a/(a+2)#
The domain of #f(a)# is #D_f(a)=RR-{-2}#
Let's do the sign chart
#color(white)(aaaa)##a##color(white)(aaaaaaa)##oo##color(white)(aaaa)##-2##color(white)(aaaaaa)##0##color(white)(aaaa)##+oo#
#color(white)(aaaa)##a+2##color(white)(aaaaaa)##-##color(white)(aa)##color(red)(∥)##color(white)(aaa)##+##color(white)(aaa)##+#
#color(white)(aaaa)##a##color(white)(aaaaaaaaaa)##-##color(white)(aa)##color(red)(∥)##color(white)(aaa)##-##color(white)(aaa)##+#
#color(white)(aaaa)##f(a)##color(white)(aaaaaaa)##+##color(white)(aa)##color(red)(∥)##color(white)(aaa)##-##color(white)(aaa)##+#
Therefore,
#f(a)>0# when #a in ] -oo,-2 [uu ] 0, +oo [#