Đáp án: Giải thích các bước giải: $A=\dfrac{1}{2.5}+\dfrac{1}{5.8}+…+\dfrac{1}{95.98}$ $ $ $=\dfrac{1}{3}.(\dfrac{3}{2.5}+\dfrac{3}{5.8}+…+\dfrac{3}{95.98})$ $ $ $=\dfrac{1}{3}.(\dfrac{1}{2}-\dfrac{1}{98})$ $ $ $=\dfrac{1}{3}.\dfrac{24}{49}$ $ $ $=\dfrac{8}{49}$ Bình luận
Ta có: $A=\dfrac{1}{2 \times 5} + \dfrac{1}{5 \times 8} + \dfrac{1}{8 \times 11} + ….. + \dfrac{1}{92 \times 95} + \dfrac{1}{95 \times 98}$ $⇔3A= \dfrac{3}{2 \times 5} + \dfrac{3}{5 \times 8} + \dfrac{3}{8 \times 11} + ….. + \dfrac{3}{92 \times 95} + \dfrac{3}{95 \times 98}$ $⇔ 3A = \dfrac{1}{2} – \dfrac{1}{98}$ $⇔ 3A = \dfrac{24}{49}$ $⇔ A = \dfrac{8}{49}$ Bình luận
Đáp án:
Giải thích các bước giải:
$A=\dfrac{1}{2.5}+\dfrac{1}{5.8}+…+\dfrac{1}{95.98}$
$ $
$=\dfrac{1}{3}.(\dfrac{3}{2.5}+\dfrac{3}{5.8}+…+\dfrac{3}{95.98})$
$ $
$=\dfrac{1}{3}.(\dfrac{1}{2}-\dfrac{1}{98})$
$ $
$=\dfrac{1}{3}.\dfrac{24}{49}$
$ $
$=\dfrac{8}{49}$
Ta có:
$A=\dfrac{1}{2 \times 5} + \dfrac{1}{5 \times 8} + \dfrac{1}{8 \times 11} + ….. + \dfrac{1}{92 \times 95} + \dfrac{1}{95 \times 98}$
$⇔3A= \dfrac{3}{2 \times 5} + \dfrac{3}{5 \times 8} + \dfrac{3}{8 \times 11} + ….. + \dfrac{3}{92 \times 95} + \dfrac{3}{95 \times 98}$
$⇔ 3A = \dfrac{1}{2} – \dfrac{1}{98}$
$⇔ 3A = \dfrac{24}{49}$
$⇔ A = \dfrac{8}{49}$