A=1/2.1/3+1/3.1/4+1/4.1/5+1/5.1/6+1/6.1/7+1/7.1/8+1/8.1/9 giúp 10/11/2021 Bởi Sadie A=1/2.1/3+1/3.1/4+1/4.1/5+1/5.1/6+1/6.1/7+1/7.1/8+1/8.1/9 giúp
Đáp án: Giải thích các bước giải: A= 1/2 -1/3+ 1/4- 1/5 +1/5-1/6 +1/6 -1/7 + 1/7 – 1/8 +1/8 -1/9 A= 1/2-1/9=7/18 Bình luận
$A=\dfrac{1}{2}.\dfrac{1}{3} + \dfrac{1}{3}.\dfrac{1}{4} + \dfrac{1}{4}.\dfrac{1}{5} +……+ \dfrac{1}{8}.\dfrac{1}{9}$ $⇔ A= \dfrac{1}{2.3}+\dfrac{1}{3.4} + \dfrac{1}{4.5}+ …….+ \dfrac{1}{8.9}$ $⇔ A = \dfrac{1}{2} – \dfrac{1}{3} + \dfrac{1}{3} – \dfrac{1}{4} + \dfrac{1}{4} – \dfrac{1}{5} + ….. + \dfrac{1}{8} – \dfrac{1}{9}$ $⇔ A = \dfrac{1}{2} – \dfrac{1}{9}$ $⇔ A = \dfrac{7}{18}$ Bình luận
Đáp án:
Giải thích các bước giải:
A= 1/2 -1/3+ 1/4- 1/5 +1/5-1/6 +1/6 -1/7 + 1/7 – 1/8 +1/8 -1/9
A= 1/2-1/9=7/18
$A=\dfrac{1}{2}.\dfrac{1}{3} + \dfrac{1}{3}.\dfrac{1}{4} + \dfrac{1}{4}.\dfrac{1}{5} +……+ \dfrac{1}{8}.\dfrac{1}{9}$
$⇔ A= \dfrac{1}{2.3}+\dfrac{1}{3.4} + \dfrac{1}{4.5}+ …….+ \dfrac{1}{8.9}$
$⇔ A = \dfrac{1}{2} – \dfrac{1}{3} + \dfrac{1}{3} – \dfrac{1}{4} + \dfrac{1}{4} – \dfrac{1}{5} + ….. + \dfrac{1}{8} – \dfrac{1}{9}$
$⇔ A = \dfrac{1}{2} – \dfrac{1}{9}$
$⇔ A = \dfrac{7}{18}$