y= 1/ln[x+√(1+x^2)]
dy/dx
=-{1/(ln[x+√(1+x^2)] )^2} . d/dx { ln[x+√(1+x^2)] }
=-{1/(ln[x+√(1+x^2)] )^2} . { 1/[x+√(1+x^2)] } .d/dx { x+√(1+x^2) }
=-{1/(ln[x+√(1+x^2)] )^2} . { 1/[x+√(1+x^2)] } . { 1+ x/√(1+x^2) }
=-{1/(ln[x+√(1+x^2)] )^2} . { 1/[x+√(1+x^2)] } . { [√(1+x^2+ x]/√(1+x^2) }
=-{1/(ln[x+√(1+x^2)] )^2} . { 1/√(1+x^2) }
= -1 / [ (ln[x+√(1+x^2)] )^2 . √(1+x^2) ]