Question

tính các giới hạn sau:

a, lim\(\frac{3.2^n-8.7^n}{4.3^n+5.7^n}\)

b, lim\(\frac{2^{n+1}\left(3.2^n-3^{n-2}\right)}{3^n\left(2^{n-1}+4\right)}\)

c, lim\(\frac{\left(-3\right)^n+2.5^n}{1-5^n}\)

d, lim\(\frac{1+2+3+...+n}{n^2+n+1}\)

Answer 1

a/ \(=lim\frac{3\left(\frac{2}{7}\right)^n-8}{4.\left(\frac{3}{7}\right)^n+5}=-\frac{8}{5}\)

b/ \(=lim\frac{6.4^n-\frac{2}{9}.6^n}{\frac{1}{2}.6^n+4.3^n}=lim\frac{6\left(\frac{4}{6}\right)^n-\frac{2}{9}}{\frac{1}{2}+4.\left(\frac{3}{6}\right)^n}=\frac{-\frac{2}{9}}{\frac{1}{2}}=-\frac{4}{9}\)

c/ \(=lim\frac{\left(-\frac{3}{5}\right)^n+2}{\left(\frac{1}{5}\right)^n-1}=\frac{2}{-1}=-2\)

d/ \(=lim\frac{n\left(n+1\right)}{2\left(n^2+n+1\right)}=lim\frac{1+\frac{1}{n}}{2+\frac{2}{n}+\frac{2}{n^2}}=\frac{1}{2}\)