Question

[lu nguyễn]

tìm các giới hạn sau:

a, \(\lim\limits_{x\rightarrow1}\frac{x^4-1}{x^3-2x^2+1}\) ( câu a,b chỉ cần thay số vào thôi đúng k ạ nếu là thay số thì k cần trình bày nữa đâu )

b, \(\lim\limits_{x\rightarrow-1}\frac{x^5+1}{x^3+1}\)

c, \(\lim\limits_{x\rightarrow3}\frac{x^3-5x^2+3x+9}{x^4-8x^2-9}\)

d, \(\lim\limits_{x\rightarrow1}\frac{x-5x^5+4x^6}{\left(1-x\right)^2}\)

e, \(\lim\limits_{x\rightarrow1}\frac{x^m-1}{x^n-1}\)

f, \(\lim\limits_{x\rightarrow-2}\frac{x^4-16}{x^3+2x^2}\)

Answer 1

[Nguyễn Việt Lâm]

\(a=\lim\limits_{x\rightarrow1}\frac{\left(x-1\right)\left(x+1\right)\left(x^2+1\right)}{\left(x-1\right)\left(x^2+x-1\right)}=\lim\limits_{x\rightarrow1}\frac{\left(x+1\right)\left(x^2+1\right)}{x^2+x-1}=\frac{4}{1}=4\)

\(b=\lim\limits_{x\rightarrow-1}\frac{\left(x+1\right)\left(x^4-x^3+x^2-x+1\right)}{\left(x+1\right)\left(x^2-x+1\right)}=\lim\limits_{x\rightarrow-1}\frac{x^4-x^3+x^2-x+1}{x^2-x+1}=\frac{5}{3}\)

\(c=\lim\limits_{x\rightarrow3}\frac{\left(x+1\right)\left(x-3\right)^2}{\left(x^2+1\right)\left(x^2-9\right)}=\lim\limits_{x\rightarrow3}\frac{\left(x+1\right)\left(x-3\right)}{\left(x^2+1\right)\left(x+3\right)}=\frac{0}{60}=0\)

\(d=\lim\limits_{x\rightarrow1}\frac{4x^6-5x^5+x}{x^2-2x+1}=\lim\limits_{x\rightarrow1}\frac{24x^5-25x^4+1}{2x-2}=\lim\limits_{x\rightarrow1}\frac{120x^4-100x^3}{2}=10\)

\(e=\lim\limits_{x\rightarrow1}\frac{mx^{m-1}}{nx^{n-1}}=\frac{m}{n}\)

\(f=\lim\limits_{x\rightarrow-2}\frac{\left(x+2\right)\left(x-2\right)\left(x^2+4\right)}{\left(x+2\right)x^2}=\lim\limits_{x\rightarrow-2}\frac{\left(x-2\right)\left(x^2+4\right)}{x^2}=-8\)

Hai câu d, e khai triển thì dài quá nên làm biếng sử dụng L'Hopital