Đáp án:
6. B
7. A
Giải thích các bước giải:
Câu 6:
$\lim\limits \dfrac{1+\dfrac{2}{5}+(\dfrac{2}{5})^{2}+...+(\dfrac{2}{5})^{n}}{1+(\dfrac{3}{4})+(\dfrac{3}{4})^{2}+....+(\dfrac{3}{4})^{n}}=\lim\limits \dfrac{1+\dfrac{\dfrac{2}{5}}{1-\dfrac{2}{5}}}{1+\dfrac{\dfrac{3}{4}}{1-\dfrac{3}{4}}}=\dfrac{5}{12}$
Câu 7: $Đề= \lim\limits_{x\to a} \dfrac{(x-1)(x-a)}{(x-a)(x^{2}+ax+a^{2})}=\lim\limits_{x\to a} \dfrac{x-1}{x^{2}+ax+a^{2}}=\dfrac{a-1}{3a^{2}}$
