1. lim (2^n-3^n).
2. lim 1+3+9+...+3^n/1+2+4+...+2^n
2 câu trả lời
Đáp án:
$1) -\infty\\ 2)+\infty.$
Giải thích các bước giải:
$1) \lim (2^n-3^n)\\ =\lim 3^n \left(\left(\dfrac{2}{3}\right)^n-1\right)\\ =\lim 3^n.\lim \left(\left(\dfrac{2}{3}\right)^n-1\right)\\ \lim 3^n=+\infty\\ \lim \left(\left(\dfrac{2}{3}\right)^n-1\right)=-1\\ \Rightarrow \lim 3^n.\lim \left(\left(\dfrac{2}{3}\right)^n-1\right)=-\infty\\ 2)\\ \lim \dfrac{1+3+9+\dots+3^n}{1+2+4+\dots+2^n}\\ =\lim \dfrac{3^0+3+3^2+\dots+3^n}{2^0+2+2^2+\dots+2^n}\\ =\lim \dfrac{\dfrac{1-3^{n+1}}{1-3}}{\dfrac{1-2^{n+1}}{1-2}}\\ =\lim \dfrac{3^{n+1}-1}{2(2^{n+1}-1)}\\ =\lim \dfrac{1-\dfrac{1}{3^{n+1}}}{2\left(\left(\dfrac{2}{3}\right)^{n+1}-\dfrac{1}{3^{n+1}}\right)}\\ =+\infty.$
Đáp án
r'l;mdwejprioeerwwrhywryerur
Giải thích các bước giải
erlkew[wkwre=ơektwkwrwerwwet
