\(B=\dfrac{4}{1\cdot4}+\dfrac{4}{4\cdot7}+...+\dfrac{4}{2014\cdot2017}\)
\(=\dfrac{4}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{2014\cdot2017}\right)\)
\(=\dfrac{4}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{2014}-\dfrac{1}{2017}\right)\)
\(=\dfrac{4}{3}\left(1-\dfrac{1}{2017}\right)=\dfrac{4}{3}\cdot\dfrac{2016}{2017}=\dfrac{8064}{6051}\)
Cho A=\(\frac{4}{1.4}+\frac{4}{4.7}+\frac{4}{7.10}+..............+\frac{4}{67.70}\)
Chứng minh A>\(\frac{9}{7}\)
Câu 1 : B = 1/3 + 1/6 + 1/10 + ... + 1/45
Câu 2 : D = 3/1.3 + 3/3.5 + 3/5.7 + ... + 3/99.101
Câu 3 : E= 4/1.3 + 4/3.5 + 5/5.7 + ... + 4/205.207
Câu 4 : F= 1/1.4 + 1/4.7 + 1/10 + ...
- tổng này có 54 số hạng
Câu 5 : G= 1/5 + 1/45 + 1/117 + 1/221
- tổng này có 54 số hạng
Bài 1 : a) -5/11.4/7+-5/11.3/7-8/11
b) (2/9:5/3+1/3:5/3)^2-(1/3-5/8)
c) 14-|-3/4|-(1/3-5/8)
Bài 2:
A= 2/1.4+2/4.7+2/7.9+...+2/196.199
Tính nhanh:
\(B=\dfrac{5}{1.4}+\dfrac{5}{4.7}+.....+\dfrac{5}{100.103}\)
a. Tính nhanh : 16 + (27 - 7 . 6) - (94 . 7 - 27 . 99)
b. Tính tổng: A = 2/1.4 + 2/4.7 + 2/7.10 + ... + 2/97.100
Tính nhanh
A=3^2/1.4+3^2/4.7+3^2/7.10+....+3^2/97.100
tính
a) P = 1 / 1.2 + 2 / 2.4 + 3 / 4.7 + ...+ 10 / 46.56
b) A= 3 / 1.2 + 3 / 2.3 + 3 / 3.4 + ....+ 3 / 99.100 chú ý : / là phần nha
c) B = 3 / 1.4 + 3 / 4.7 + 3 / 7.10 + ... + 3 / 100.103
d) C= 5 / 1.4 + 5 / 4.7 + 5 / 7.10 + ...+ 5 / 100.103
e) D= 7 / 1.5 + 7 / 5.9 + 7 / 9.13 +...+ 7 / 101.105
tinh tong :
\(\dfrac{3}{1.4}\) + \(\dfrac{3}{4.7}\) + \(\dfrac{3}{7.10}\) +.............+\(\dfrac{3}{94.97}\)
5 Tinh tong
S=\(\dfrac{3}{1.4}\)+\(\dfrac{3}{4.7}\)+\(\dfrac{3}{7.10}\)+...+\(\dfrac{3}{97.100}\)
