Tìm tất cả các giá trị của tham số a để \(lim\dfrac{n^4-3n+4}{an^3+2n^2+1}=-\infty\)
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Những câu hỏi liên quan
MH
13 tháng 10 2023
1) \(\lim\limits_{n\rightarrow\infty}\dfrac{6n-8}{n-1}=\lim\limits_{n\rightarrow\infty}\dfrac{2n\left(1-\dfrac{4}{n}\right)}{n\left(1-\dfrac{1}{n}\right)}=2\)
2) \(\lim\limits_{n\rightarrow\infty}\dfrac{n^2+5n-3}{4n^3-2n+5}=\lim\limits_{n\rightarrow\infty}\dfrac{n^2\left(1+\dfrac{5}{n}-\dfrac{3}{n^2}\right)}{n^3\left(4-\dfrac{2}{n^2}+\dfrac{5}{n^3}\right)}=\dfrac{1}{4n}=\infty\)
3) \(\lim\limits_{n\rightarrow\infty}\left(-2n^5+4n^4-3n^2+4\right)=\lim\limits_{n\rightarrow\infty}n^5\left(-2+\dfrac{4}{n}-\dfrac{3}{n^2}+\dfrac{4}{n^5}\right)=-2n^5=-\infty\)
NV
Nguyễn Việt Lâm
Giáo viên
21 tháng 1 2021
1.
Gọi \(d=ƯC\left(2n^2+3n+1;3n+1\right)\)
\(\Rightarrow2n^2+3n+1-\left(3n+1\right)⋮d\)
\(\Rightarrow2n^2⋮d\Rightarrow2n\left(3n+1\right)-3.2n^2⋮d\)
\(\Rightarrow2n⋮d\Rightarrow2\left(3n+1\right)-3.2n⋮d\Rightarrow2⋮d\Rightarrow\left[{}\begin{matrix}d=1\\d=2\end{matrix}\right.\)
\(d=2\Rightarrow3n+1=2k\Rightarrow n=2m+1\)
\(\Rightarrow n\) lẻ thì A không tối giản
\(\Rightarrow n\) chẵn thì A tối giản
NV
Nguyễn Việt Lâm
Giáo viên
21 tháng 1 2021
2.
Giả thiết tương đương:
\(xy^2+\dfrac{x^2}{z}+\dfrac{y}{z^2}=3\)
Đặt \(\left(x;y;\dfrac{1}{z}\right)=\left(a;b;c\right)\Rightarrow a^2c+b^2a+c^2b=3\)
Ta có: \(9=\left(a^2c+b^2a+c^2b\right)^2\le\left(a^4+b^4+c^4\right)\left(c^2+a^2+b^2\right)\)
\(\Rightarrow9\le\left(a^4+b^4+c^4\right)\sqrt{3\left(a^4+b^4+c^4\right)}\)
\(\Rightarrow3\left(a^4+b^4+c^4\right)^3\ge81\Rightarrow a^4+b^4+c^4\ge3\)
\(\Rightarrow M=\dfrac{1}{a^4+b^4+c^4}\le\dfrac{1}{3}\)
\(M_{max}=\dfrac{1}{3}\) khi \(\left(a;b;c\right)=\left(1;1;1\right)\) hay \(\left(x;y;z\right)=\left(1;1;1\right)\)
HT
6 tháng 2 2021
\(a=\lim\limits\dfrac{3n^3-2n+1}{4n^4+2n+1}=\lim\limits\dfrac{\dfrac{3n^3}{n^4}-\dfrac{2n}{n^4}+\dfrac{1}{n^4}}{\dfrac{4n^4}{n^4}+\dfrac{2n}{n^4}+\dfrac{1}{n^4}}=0\)
\(\Rightarrow\lim\limits\dfrac{-2n^2+1}{-n^2+3n+3}=\lim\limits\dfrac{-\dfrac{2n^2}{n^2}+\dfrac{1}{n^2}}{-\dfrac{n^2}{n^2}+\dfrac{3n}{n^2}+\dfrac{3}{n^2}}=-\dfrac{2}{-1}=2\)
15 tháng 10 2023
1:
\(\lim\limits_{n\rightarrow\infty}\dfrac{-3n^3+3n^2-1}{n^2-2n}=\lim\limits_{n\rightarrow\infty}\dfrac{n^3\left(-3+\dfrac{3}{n}-\dfrac{1}{n^3}\right)}{n^2\left(1-\dfrac{2}{n}\right)}\)
\(=\lim\limits_{n\rightarrow\infty}\dfrac{-3n^3}{n^2}=\lim\limits_{n\rightarrow\infty}-3n=-\infty\)
2:
\(\lim\limits_{n\rightarrow\infty}\dfrac{3n^2-1}{-2n+3}=\lim\limits_{n\rightarrow\infty}\dfrac{n^2\left(3-\dfrac{1}{n^2}\right)}{n\left(-2+\dfrac{3}{n}\right)}\)
\(=\lim\limits_{n\rightarrow\infty}\dfrac{-3}{2}n=-\infty\)
15 tháng 10 2023
1:
\(\lim\limits_{n\rightarrow\infty}\dfrac{3n^5+3n^3-1}{n^3-2n}=\lim\limits_{n\rightarrow\infty}\dfrac{n^5\left(3+\dfrac{3}{n^2}-\dfrac{1}{n^5}\right)}{n^3\left(1-\dfrac{2}{n^2}\right)}\)
\(=\lim\limits_{n\rightarrow\infty}n^2\cdot3=+\infty\)
2: \(\lim\limits_{n\rightarrow\infty}\dfrac{3n^7+3n^5-n}{3n^2-2n}=\lim\limits_{n\rightarrow\infty}\dfrac{3n^6+3n^4-1}{3n-2}\)
\(=\lim\limits_{n\rightarrow\infty}\dfrac{n^6\left(3+\dfrac{3}{n^2}-\dfrac{1}{n^6}\right)}{n\left(3-\dfrac{2}{n}\right)}=\lim\limits_{n\rightarrow\infty}n^5=+\infty\)
24 tháng 11 2023
1: \(\lim\limits_{n\rightarrow\infty}\left(-2n^5+4n^4-3n^2+4\right)\)
\(=\lim\limits_{n\rightarrow\infty}\left[n^5\left(-2+\dfrac{4}{n}-\dfrac{3}{n^3}+\dfrac{4}{n^5}\right)\right]\)
\(=-\infty\) vì \(\left\{{}\begin{matrix}\lim\limits_{n\rightarrow\infty}n^5=+\infty\\\lim\limits_{n\rightarrow\infty}\left(-2+\dfrac{4}{n}-\dfrac{3}{n^3}+\dfrac{4}{n^5}\right)=-2< 0\end{matrix}\right.\)
2: \(\lim\limits_{n\rightarrow\infty}\dfrac{-3n^2+2}{n-2}\)
\(=\lim\limits_{n\rightarrow\infty}\dfrac{n^2\left(-3+\dfrac{2}{n^2}\right)}{n\left(1-\dfrac{2}{n}\right)}\)
\(=\lim\limits_{n\rightarrow\infty}\dfrac{n\left(-3+\dfrac{2}{n^2}\right)}{1-\dfrac{2}{n}}\)
\(=-\infty\) vì \(\lim\limits_{n\rightarrow\infty}n=+\infty;\lim\limits_{n\rightarrow\infty}\dfrac{-3+\dfrac{2}{n^2}}{1-\dfrac{2}{n}}=-\dfrac{3}{1}=-3< 0\)
MH
12 tháng 2 2022
\(a,lim\dfrac{2n^2+1}{3n^3-3n+3}\)
\(=lim\dfrac{\dfrac{2}{n}+\dfrac{1}{n^3}}{3-\dfrac{3}{n^2}+\dfrac{3}{n^3}}=0\)
NV
Nguyễn Việt Lâm
Giáo viên
12 tháng 2 2022
\(\lim\dfrac{-3n^3+1}{2n+5}=\lim\dfrac{-3n^2+\dfrac{1}{n}}{2+\dfrac{5}{n}}=\dfrac{-\infty}{2}=-\infty\)
\(\lim\dfrac{n^3-2n+1}{-3n-4}=\lim\dfrac{n^2-2+\dfrac{1}{n}}{-3-\dfrac{4}{n}}=\dfrac{+\infty}{-3}=-\infty\)
Y
15 tháng 10 2023
\(1,\lim\limits_{n\rightarrow\infty}\dfrac{-n^2+2n+1}{\sqrt{3n^4+2}}\left(1\right)\)
\(\dfrac{-n^2+2n+1}{\sqrt{3n^4+2}}=\dfrac{-\dfrac{n^2}{n^4}+\dfrac{2n}{n^4}+\dfrac{1}{n^4}}{\sqrt{\dfrac{3n^4}{n^4}+\dfrac{2}{n^4}}}=\dfrac{-\dfrac{1}{n^2}+\dfrac{2}{n^3}+\dfrac{1}{n^4}}{\sqrt{3+\dfrac{2}{n^4}}}\)
\(\Rightarrow\left(1\right)=\dfrac{-lim\dfrac{1}{n^2}+2lim\dfrac{1}{n^3}+lim\dfrac{1}{n^4}}{\sqrt{lim\left(3+\dfrac{2}{n^4}\right)}}\)
\(=\dfrac{0}{\sqrt{lim\left(3+\dfrac{2}{n^4}\right)}}=0\)
\(2,\lim\limits_{n\rightarrow\infty}\left(\dfrac{4n-\sqrt{16n^2+1}}{n+1}\right)\left(2\right)\)
\(\dfrac{4n-\sqrt{16n^2+1}}{n+1}=\dfrac{\dfrac{4n}{n^2}-\sqrt{\dfrac{16n^2}{n^2}+\dfrac{1}{n^2}}}{\dfrac{n}{n^2}+\dfrac{1}{n^2}}=\dfrac{\dfrac{4}{n}-\sqrt{16+\dfrac{1}{n^2}}}{\dfrac{1}{n}+\dfrac{1}{n^2}}\)
\(\Rightarrow\left(2\right)=\dfrac{lim\left(\dfrac{4}{n}-\sqrt{16+\dfrac{1}{n^2}}\right)}{lim\left(\dfrac{1}{n}+\dfrac{1}{n^2}\right)}=\dfrac{lim\left(\dfrac{4}{n}-\sqrt{16+\dfrac{1}{n^2}}\right)}{0}\)
Vậy giới hạn \(\left(2\right)\) không xác định.
\(3,\lim\limits_{n\rightarrow\infty}\left(\dfrac{\sqrt{9n^2+n+1}-3n}{2n}\right)\left(3\right)\)
\(\dfrac{\sqrt{9n^2+n+1}-3n}{2n}=\dfrac{\sqrt{9+\dfrac{1}{n}+\dfrac{1}{n^2}}-\dfrac{3}{n}}{\dfrac{2}{n}}\)
\(\Rightarrow\left(3\right)=\dfrac{lim\left(\sqrt{9+\dfrac{1}{n}+\dfrac{1}{n^2}}-\dfrac{3}{n}\right)}{2lim\dfrac{1}{n}}=\dfrac{lim\left(\sqrt{9+\dfrac{1}{n}+\dfrac{1}{n^2}}-\dfrac{3}{n}\right)}{0}\)
Vậy \(lim\left(3\right)\) không xác định.
\(\lim\dfrac{n^4-3n+4}{an^3+2n^2+1}=\lim\dfrac{n-\dfrac{3}{n^2}+\dfrac{4}{n^3}}{a+\dfrac{2}{n}+\dfrac{1}{n^3}}=+\infty.\left(\dfrac{1}{a}\right)\)
Giới hạn đã cho bằng \(-\infty\) khi và chỉ khi \(\dfrac{1}{a}< 0\Leftrightarrow a< 0\)
Em muốn hỏi thêm bài này ạ
Tìm tất cả các giá trị của m để PT có nghiệm:\(\left(2m^2-5m+2\right)\left(x-1\right)^{2021}\left(x^{2020}-2\right)+2x^2... - Hoc24