Question

大一高数题，帮下忙

Answer 1

解：lim(x+a)/(x-a)=lim{1+[2a/(x-a)]}^x
x→∞ x→∞
=lim{1+1/[(x-a)/2a]}^([(x-a)/(2a)]*[2ax/(x-a)]}
x→∞
=lim【{1+1/[(x-a)/2a]}^[(x-a)/2a]】^[2ax/(x-a)]
x→∞
=e^lim{2a+[2a^2/(x-a)]}
x→∞
=e^2a
又lim(x+a)/(x-a)=9
x→∞
∴e^2a=9
2a=ln9
a=ln3

追问

谢谢

追答

解：原式=lim[1+(x+1)/x^2]^x
x→∞
=lim{1+1/[x^2/(x+1)]}^[x^2/(x+1)]*[(x+1)/x]
x→∞
=e^{lim[(x+1)/x]}
x→∞
=e^lim[1+(1/x)]
x→∞
=e

Answer 2

追问

谢谢，麻烦在帮一题

追答

追问

追答

Answer 3

大一的时候会，现在不会了