Let   fx=x+12-1,x≥-1 Then the set x:fx=f-1x is

Since fx=x+12-1is continuous function, solution of fx=f-1x lies on the line y: x. Therefore,         fx=f-1x=xor     x+12-1=xor     x2+x=0i.e.,   x=0    or  -1Therefore, the required set is {0, - 1}.