Bạn chưa đăng nhập. Vui lòng đăng nhập để hỏi bài

Những câu hỏi liên quan
Hoàng Hoài An
Xem chi tiết
soyeon_Tiểu bàng giải
12 tháng 8 2016 lúc 15:51

\(\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+\frac{1}{130}+\frac{1}{208}\)

\(=\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+\frac{1}{13.16}\)

\(=\frac{1}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\right)\)

\(=\frac{1}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\right)\)

\(=\frac{1}{3}.\left(1-\frac{1}{16}\right)\)

\(=\frac{1}{3}.\frac{15}{16}=\frac{5}{16}\)

Big Boss
12 tháng 8 2016 lúc 15:55

1/1.4+1/4.7+1/7.10+..+1/13.16

1-1/4+1/4-1/7+..+1/13-1/16

1-1/16

15/16

Đỗ Hoàng Phương Dung
Xem chi tiết
Phạm Trung Hải
21 tháng 9 2015 lúc 18:02

=13/16

cách của mình ngắn gọn hơn cơ

Đỗ Yến Linh
Xem chi tiết
Vi Thị Vinh
16 tháng 7 2023 lúc 20:57

5,055...X_X

 

Hoang Thi Khanh Linh
Xem chi tiết
Song Ngư
7 tháng 11 2018 lúc 11:41

\(\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+\frac{1}{130}+\frac{1}{208}\)

\(=\frac{1}{1\times4}+\frac{1}{4\times7}+\frac{1}{7\times10}+\frac{1}{10\times13}+\frac{1}{13\times16}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\)

\(=1-\frac{1}{16}=\frac{15}{16}\)

Chúc bạn học tốt ^^

Thanh Bá
27 tháng 12 2021 lúc 14:03

1+100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000=1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Khách vãng lai đã xóa
bui thi thanh
Xem chi tiết
Trần Hữu Tín
22 tháng 3 2017 lúc 14:30

1/2A=1/2(6/4+6/28+6/70+6/130+6/208)

       = 3/4+3/28+3/70+3/130+3/208

       = 1-1/4+1/4-1/7+..................-1/16

       =1-1/16

       =15/16 => A=15/8

lê hùng hưng
Xem chi tiết
cô bé đenn xì :
Xem chi tiết
Nguyễn Đức Trí
26 tháng 8 2023 lúc 12:52

\(A=\dfrac{2}{1x3}+\dfrac{2}{3x5}+\dfrac{2}{5x7}+...+\dfrac{2}{21x23}\)

\(A=2x\left(\dfrac{1}{1x3}+\dfrac{1}{3x5}+\dfrac{1}{5x7}+...+\dfrac{1}{21x23}\right)\)

\(A=2x\dfrac{1}{2}x\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{21}-\dfrac{1}{23}\right)\)

\(A=1-\dfrac{1}{23}\)

\(A=\dfrac{22}{23}\)

Nguyễn Đức Trí
26 tháng 8 2023 lúc 12:57

\(B=\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}\)

\(B=\dfrac{1}{2x3}+\dfrac{1}{3x4}+\dfrac{1}{4x5}+\dfrac{1}{5x6}+\dfrac{1}{6x7}+\dfrac{1}{7x8}+\dfrac{1}{8x9}+\dfrac{1}{9x10}\)

\(B=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)

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

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

\(B=\dfrac{4}{10}\)

\(B=\dfrac{2}{5}\)

Nguyễn Đức Trí
26 tháng 8 2023 lúc 13:02

\(C=\dfrac{1}{28}+\dfrac{1}{70}+\dfrac{1}{130}+\dfrac{1}{208}\)

\(C=\dfrac{1}{4x7}+\dfrac{1}{7x10}+\dfrac{1}{10x13}+\dfrac{1}{13x16}\)

\(C=\dfrac{1}{3}x\left(\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{16}\right)\)

\(C=\dfrac{1}{3}x\left(\dfrac{1}{4}-\dfrac{1}{16}\right)\)

\(C=\dfrac{1}{3}x\left(\dfrac{4}{16}-\dfrac{1}{16}\right)\)

\(C=\dfrac{1}{3}x\dfrac{3}{16}\)

\(C=\dfrac{1}{16}\)

Khuất Hữu Khang Einstein
Xem chi tiết
Đặng Cường Thành
19 tháng 4 2020 lúc 16:57

\(3M=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{97.100}\)

\(3M=\frac{4-1}{1.4}+\frac{7-4}{4.7}+...+\frac{100-97}{97.100}\)

\(3M=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{100}\)

\(3M=1-\frac{1}{100}\)

\(3M=\frac{99}{100}\)

\(M=\frac{33}{100}\)

Mạc Văn Thắng
Xem chi tiết
ZORO
15 tháng 9 2017 lúc 15:17

M=1/4+1/4.7+1/7.10+1/10.13+.............+1/88.91

3M=3/4+3/4.7+3/7.10+3/10.13+........+3/88.91

3M= 3/4+1/4-1/7+1/7-1/10+1/10-1/13+......+1/88-1/91

3M=3/4+1/4-1/91=1-1/91=90/91 

----->M= 30/91