If f(x)=xtan−1x then limx→1 f(x)−f(1)x−1=
π4
π+14
π+24
π+34
Ltx→1fx−f1x−1=Ltx→1xtan−1x−π/4x−1=Ltx→1x1+x2+tan−1x1=12+π4=π+24.