第1个回答 2023-07-29
√(1+ x^2) = 1+ (1/2)x^2 +o(x^3)
x+√(1+ x^2) = 1+ x+ (1/2)x^2 +o(x^3)
ln(x+√(1+ x^2))
=[x+ (1/2)x^2] - (1/2)[x+ (1/2)x^2]^2 +(1/3)[x+ (1/2)x^2]^3 +o(x^3)
=[x+ (1/2)x^2] - (1/2)[x^2+ x^3+...] +(1/3)[x^3+...] +o(x^3)
=x -(1/6)x^3 +o(x^3)