Limit [(Sin[x] - Tan[x])/(Sqrt[1 + x^2] - 1) (Sqrt[1 + Sin[x]^2] - 1),x -> 0]
= Limit [(Sin[x] - Tan[x])/(Sqrt[1 + x^2] - 1) (Sqrt[1 + x^2] - 1),x -> 0]
= Limit [Sin[x] - Tan[x],x -> 0]
= Limit [(Cos[x]Sin[x] - Sin[x])/Cos[x],x -> 0]
= Limit [((Cos[x] – 1) Sin[x])/Cos[x],x -> 0]
= Limit [(0×0/1,x -> 0]
= 0