If the function f:1,∞→1,∞ is defined by fx=2xx-1 then f-1x is
12xx-1
121+1+4log2x
121-1+4log2x
not defined
y=2xx-1 or x2-x-log2y=0or x=121±1+4log2ysince x∈1,∞, we choose x=121+1+4log2yor f-1x=121+1+4log2x.