Đáp án:
`lim\frac{3^n-2^{2n+1}}{2^{2n}+ 2^n}=-2`
Giải thích các bước giải:
`lim\frac{3^n-2^{2n+1}}{2^{2n}+ 2^n}`
`=lim\frac{3^n-2^{2n}.2}{2^{2n}+ 2^n}`
`=lim\frac{3^n-4^{n}.2}{4^{n}+ 2^n}`
`=lim\frac{4^n.(3^n/(4^n)-2)}{4^{n}.(1+ 2^n/4^n)}`
`=lim\frac{(3/4)^n-2}{1+ (2/4)^n}`
`=\frac{0-2}{1+ 0}=(-2)/1=-2`
Kết luận: `lim\frac{3^n-2^{2n+1}}{2^{2n}+ 2^n}=-2`