Question

[nguyen diep anh]

bai 1 tinh nhanh

a . 1/5x6 +1/6x7+ 1/7x8 + 1/8x9 +1/9x10

b . 1/1x2 + 1/2x3 + ....... + 1/99x100

c . 2/3x5 + 2/5x7 + 2/7x8 + 2/8x9

d . 2/3x5 + 2/5x7 + .......+ 2/98x100

bai 2 tinh hop li

9/13 + 14/6 + 1/9 + 4/6 + 7/13 + 17/19

bai 3 dien dau ( > , < , = )

a . 3/4 + 5/2 ....... 5/8 + 2 3/5 ( hon so )

B . 3 1/5 - 8/3 ......... 17/5 - 2 12/5 hon so

c . 2 4/9 + 18/7......... 22/9 + 2 4/7

giup mk nha cac ban , mai mk phai nop bai roi toi nay mk se lay y kien cua cac ban , giup mk nha

Answer 1

[Cuber Việt]

b1

a) \(\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}\)

\(=\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)

\(=\dfrac{1}{5}-\dfrac{1}{10}\)

\(=\dfrac{2}{10}-\dfrac{1}{10}\)

\(=\dfrac{1}{10}\)

b) \(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}\)

\(=\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{99}-\dfrac{1}{100}\)

\(=\dfrac{1}{1}-\dfrac{1}{100}\)

\(=\dfrac{99}{100}\)

c) \(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}\)

\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\)

\(=\dfrac{1}{3}-\dfrac{1}{11}\)

\(=\dfrac{8}{33}\)

d) \(\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{99.101}\)

\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{99}-\dfrac{1}{101}\)

\(=\dfrac{1}{3}-\dfrac{1}{101}\)

\(=\dfrac{98}{303}\)

Answer 2

[nguyen diep anh]

ban lam bai 2 va 3 nua nha ♥♥♥