f:[1,∞)→[2,∞),f(x)=x+1x,then  f−1(x)=

Interchanging x and y, x=y+1y ⇒y2−xy+1=0⇒y=x±x2−42=f−1(x) Put, f−1(5)=5−14<1, if negative sign is used∴f−1(x)=x+x2−42