lim \(\frac{\left(3-5n\right)^2\left(n+2\right)^2}{1-7n+10n^4}\)
K
Khách
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NV
Nguyễn Việt Lâm
Giáo viên
11 tháng 2 2020
a/ \(=lim\frac{\left(-\frac{2}{3}\right)^n+1}{-2.\left(-\frac{2}{3}\right)^n+3}=\frac{1}{3}\)
b/ \(=lim\frac{\left(2-\frac{1}{n}\right)\left(1+\frac{1}{n}\right)\left(3+\frac{4}{n}\right)}{\left(\frac{5}{n}-6\right)^3}=\frac{2.1.3}{\left(-6\right)^3}=-\frac{1}{36}\)
c/ \(=lim\frac{5n+3}{\sqrt{n^2+5n+1}+\sqrt{n^2-2}}=\frac{5+\frac{3}{n}}{\sqrt{1+\frac{5}{n}+\frac{1}{n^2}}+\sqrt{1-\frac{2}{n}}}=\frac{5}{1+1}=\frac{5}{2}\)
d/ \(=lim\frac{5.\left(\frac{1}{2}\right)^n-6}{4.\left(\frac{1}{3}\right)^n+1}=\frac{-6}{1}=-6\)
e/ \(=-n^3\left(2+\frac{3}{n}-\frac{5}{n^2}+\frac{2020}{n^3}\right)=-\infty.2=-\infty\)
AH
Akai Haruma
Giáo viên
10 tháng 4 2020
1.
\(\lim \frac{3n^2+5n+4}{2-n^2}=\lim \frac{\frac{3n^2+5n+4}{n^2}}{\frac{2-n^2}{n^2}}=\lim \frac{3+\frac{5}{n}+\frac{4}{n^2}}{\frac{2}{n^2}-1}=\frac{3}{-1}=-3\)
2.
\(\lim \frac{2n^3-4n^2+3n+7}{n^3-7n+5}=\lim \frac{\frac{2n^3-4n^2+3n+7}{n^3}}{\frac{n^3-7n+5}{n^3}}=\lim \frac{2-\frac{4}{n}+\frac{3}{n^2}+\frac{7}{n^3}}{1-\frac{7}{n^2}+\frac{5}{n^3}}=\frac{2}{1}=2\)
3.
\(\lim (\frac{2n^3}{2n^2+3}+\frac{1-5n^2}{5n+1})=\lim (n-\frac{3n}{2n^2+3}+\frac{1}{5}-n-\frac{1}{5n+1})\)
\(=\frac{1}{5}-\lim (\frac{3n}{2n^2+3}+\frac{1}{5n+1})=\frac{1}{5}-\lim (\frac{3}{2n+\frac{3}{n}}+\frac{1}{5n+1})=\frac{1}{5}-0=\frac{1}{5}\)
4.
\(\lim \frac{1+3^n}{4+3^n}=\lim (1-\frac{3}{4+3^n})=1-\lim \frac{3}{4+3^n}=1-0=1\)
5.
\(\lim \frac{4.3^n+7^{n+1}}{2.5^n+7^n}=\lim \frac{\frac{4.3^n+7^{n+1}}{7^n}}{\frac{2.5^n+7^n}{7^n}}\)
\(=\lim \frac{4.(\frac{3}{7})^n+7}{2.(\frac{5}{7})^n+1}=\frac{7}{1}=7\)
NV
Nguyễn Việt Lâm
Giáo viên
2 tháng 1 2019
\(lim\left(5n-\sqrt{25n^2-3n+5}\right)=lim\dfrac{25n^2-25n^2+3n-5}{5n+\sqrt{25n^2-3n+5}}\)
\(=lim\dfrac{3n-5}{5n+\sqrt{25n^2-3n+5}}=lim\dfrac{3-\dfrac{5}{n}}{5+\sqrt{25-\dfrac{3}{n}+\dfrac{5}{n^2}}}=\dfrac{3-0}{5+\sqrt{25-0+0}}=\dfrac{3}{10}\)
\(lim\dfrac{4n^5-3n^4-2n^3+7n-9}{-5n\left(3n^2-3n+1\right)\left(5-2n^2\right)}=lim\dfrac{\dfrac{4n^5-3n^4-2n^3+7n-9}{n^5}}{\dfrac{-5n}{n}\dfrac{\left(3n^2-3n+1\right)}{n^2}\dfrac{\left(5-2n^2\right)}{n^2}}\)
\(=lim\dfrac{4-\dfrac{3}{n}-\dfrac{2}{n^2}+\dfrac{7}{n^4}-\dfrac{9}{n^5}}{-5.\left(3-\dfrac{2}{n}+\dfrac{1}{n^2}\right).\left(\dfrac{5}{n^2}-2\right)}=\dfrac{4-0-0+0-0}{-5\left(3-0+0\right).\left(0-2\right)}=\dfrac{2}{15}\)
NV
Nguyễn Việt Lâm
Giáo viên
1 tháng 3 2020
\(=lim\frac{2.2^{5n}+3}{9.3^{5n}+1}=lim\frac{2.\left(\frac{2}{3}\right)^{5n}+3\left(\frac{1}{3}\right)^{5n}}{9+\left(\frac{1}{3}\right)^{5n}}=\frac{0}{9}=0\)
\(b=lim\frac{\left(-\frac{1}{3}\right)^n+4}{-1\left(-\frac{1}{3}\right)^n-2}=\frac{4}{-2}=-2\)
\(c=1+lim\frac{-n}{n^2+\sqrt{n^4+n}}=1+lim\frac{-\frac{1}{n}}{1+\sqrt{1+\frac{1}{n^3}}}=1+\frac{0}{2}=1\)
\(-2\le2cosn^2\le2\Rightarrow\frac{-2}{n^2+1}\le\frac{2cosn^2}{n^2+1}\le\frac{2}{n^2+1}\)
Mà \(lim\frac{-2}{n^2+1}=lim\frac{2}{n^2+1}=0\Rightarrow lim\frac{2cosn^2}{n^2+1}=0\)
\(d=lim\left[n\left(\sqrt{1-\frac{2}{n^2}}-1+1-\sqrt[3]{1+\frac{2}{n^2}}\right)\right]\)
\(=lim\left[n\left(\frac{-\frac{2}{n^2}}{\sqrt{1-\frac{2}{n^2}}+1}-\frac{\frac{2}{n^2}}{\sqrt[3]{\left(1+\frac{2}{n^2}\right)^2}+\sqrt[3]{1+\frac{2}{n^2}}+1}\right)\right]\)
\(=lim\left(\frac{-\frac{2}{n}}{\sqrt{1-\frac{2}{n^2}}+1}-\frac{\frac{2}{n}}{\sqrt[3]{\left(1+\frac{2}{n^2}\right)^2}+\sqrt[3]{1+\frac{2}{n^2}}+1}\right)=\frac{0}{2}-\frac{0}{1+1+1}=0\)
NV
Nguyễn Việt Lâm
Giáo viên
19 tháng 2 2020
a/ \(=lim\frac{1}{\sqrt{n+1}+\sqrt{n}}=\frac{1}{\infty}=0\)
b/ \(=lim\frac{6n+1}{\sqrt{n^2+5n+1}+\sqrt{n^2-n}}=\frac{6+\frac{1}{n}}{\sqrt{1+\frac{5}{n}+\frac{1}{n^2}}+\sqrt{1-\frac{1}{n}}}=\frac{6}{1+1}=3\)
c/ \(=lim\frac{6n-9}{\sqrt{3n^2+2n-1}+\sqrt{3n^2-4n+8}}=lim\frac{6-\frac{9}{n}}{\sqrt{3+\frac{2}{n}-\frac{1}{n^2}}+\sqrt{3-\frac{4}{n}+\frac{8}{n^2}}}=\frac{6}{\sqrt{3}+\sqrt{3}}=\sqrt{3}\)
d/ \(=lim\frac{\left(\frac{2}{6}\right)^n+1-4\left(\frac{4}{6}\right)^n}{\left(\frac{3}{6}\right)^n+6}=\frac{1}{6}\)
NV
Nguyễn Việt Lâm
Giáo viên
19 tháng 2 2020
e/ \(=lim\frac{\left(\frac{3}{5}\right)^n-\left(\frac{4}{5}\right)^n+1}{\left(\frac{3}{5}\right)^n+\left(\frac{4}{5}\right)^n-1}=\frac{1}{-1}=-1\)
f/ Ta có công thức:
\(1+3+...+\left(2n+1\right)^2=\left(n+1\right)^2\)
\(\Rightarrow lim\frac{1+3+...+2n+1}{3n^2+4}=lim\frac{\left(n+1\right)^2}{3n^2+4}=lim\frac{\left(1+\frac{1}{n}\right)^2}{3+\frac{4}{n^2}}=\frac{1}{3}\)
g/ \(=lim\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{n}-\frac{1}{n+1}\right)=lim\left(1-\frac{1}{n+1}\right)=1-0=1\)
h/ Ta có: \(1^2+2^2+...+n^2=\frac{n\left(n+1\right)\left(2n+1\right)}{6}\)
\(\Rightarrow lim\frac{n\left(n+1\right)\left(2n+1\right)}{6n\left(n+1\right)\left(n+2\right)}=lim\frac{2n+1}{6n+12}=lim\frac{2+\frac{1}{n}}{6+\frac{12}{n}}=\frac{2}{6}=\frac{1}{3}\)
11 tháng 4 2020
a) lim \(\frac{\left(2n+1\right)^2\left(n-1\right)}{\sqrt[3]{n^3+7n-2}}\)
= lim \(\left(2n+1\right)^2.\frac{\left(1-\frac{1}{n}\right)}{\sqrt[3]{1+\frac{7}{n^2}-\frac{2}{n^3}}}\)
\(=+\infty\)
b) lim \(\left(2n-1\right)\sqrt{\frac{2n^2+5}{n^4+n^2+2}}\)
= lim \(\left(2-\frac{1}{n}\right)\sqrt{\frac{2+\frac{5}{n^2}}{1+\frac{1}{n^2}+\frac{2}{n^4}}}\)
=2.2 = 4
c ) = lim \(n.\frac{n^2}{\sqrt[3]{\left(n^3+n^2\right)^2+n\sqrt[3]{n^3+n^2}+n^2}}\)
= lim \(n.\frac{1}{\sqrt[3]{\left(1+\frac{1}{n}\right)^2+\sqrt[3]{1+\frac{1}{n}}+1}}\)
\(=+\infty\)
NV
Nguyễn Việt Lâm
Giáo viên
22 tháng 2 2020
\(=lim\frac{3+\frac{2}{n}+\frac{5}{n^2}}{7+\frac{1}{n}-\frac{8}{n^2}}=\frac{3}{7}\)
\(=lim-3n^3\left(1-\frac{5}{3n^2}+\frac{2}{3n^3}\right)=-\infty\)
\(=lim\frac{\left(\frac{3}{7}\right)^n+4}{3-2.\left(\frac{1}{7}\right)^n}=\frac{4}{3}\)
Câu này đề thiếu, giới hạn của x nên nó là giới hạn của hàm chứ ko phải giới hạn của dãy, mà giới hạn của hàm thì cần chỉ rõ x tiến tới bao nhiêu mới tính được
\(=lim\frac{\left(\frac{1}{3}\right)^n-1}{\left(\frac{2}{3}\right)^n+4}=-\frac{1}{4}\)
O
1
NM
20 tháng 1 2021
\(lim\dfrac{\left(n-1\right)^2.\left(7n+2\right)^n}{\left(2n+1\right)^4}\)
\(=lim\dfrac{n^4.\left(\dfrac{1}{n}-\dfrac{1}{n^2}\right).n^n.\left(7+\dfrac{2}{n}\right)^n}{n^4\left(2+\dfrac{1}{n}\right)^4}\)
\(=\dfrac{0}{2}=0\)
mình làm hơi gọn, bạn kh hiểu thì hỏi mình nha
\(=lim\frac{\left(\frac{3-5n}{n}\right)^2\left(\frac{n+2}{n}\right)^2}{\frac{1-7n+10n^4}{n^4}}=lim\frac{\left(\frac{3}{n}-5\right)^2\left(1+\frac{2}{n}\right)^2}{\frac{1}{n^4}-\frac{7}{n^3}+10}=\frac{\left(-5\right)^2.1^2}{10}=\frac{5}{2}\)