a)6/1.4+6/4.7+6/7.10+....+6/97.100
b 4/1.3+16/3.5+36/5.7+.....+9604/97.99
c (1/1.2+1/3.4+1/5.6+...........+1/19.20)-(1/11+1/12+.....+1/20)
Tính các tổng sau
1 :D = 1.3 +2.3+3.4+........+99.100
2 . E= 1.3 +3.5+5.7+.........+97.99
3.F= 2.4 + 4.6+ 6+8+..........+98.1009
4. G=1.4+2.5+3.6+........+97.100
Giúp mình nhé . Mình cần gấp
Bài 1:Tính:
a,3 14/19 + 13/17 + 35/43 + 6 5/19 + 8/13
b,130 25/28 + 120 17/35
c,17 2/31 - (15/17 + 6 2/31)
d,(31 6/13 + 5 9/41) - 31 6/13
e,(17 24/31 - 3 7/8) - (2 38/31 - 4)
g,1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6
h,1/1.2 + 1/2.3 + 1/3.4 + .........+ 1/49.100
i,1/1.3 + 1/3.5 + 1/5.7 +........+ 1/97.99
A=1/1.2+1/2.3+1/3.4+....+1/50.51
B=2/3.5+2/5.7+2/7.9+....+2/51.53
C=6/4.7+6/7.10+6/10.13+....+6/73.76
GIÚP MIK VỚI CẢM ƠN MN.
A = 1 /1.2 + 1/ 2.3 + 1 /3.4 + . . . + 1/ 49.50 + 1/ 50.51
A = 2 − 1/ 1.2 + 3 − 2 /2.3 + 4 − 3 /3.4 + . . . + 50 − 49 /49.50 + 51 − 50/ 50.51
A = 1 − 1/ 2 + 1/ 2 − 1 /3 + 1 /3 − 1/ 4 + . . . + 1 /50 − 1 /51
A=1-1/51
A=50/51
B=6/4.7+6/7.10+6/10.13+...+6/73.76
=2.(3/4.7 +3/7.10 +3/10.13 +...+3/73.76 )
=2.(1/4 −1/7 +1/7 −1/10 +1/10 −1/13 +...+1/73 −1/76 )
=2.(1/4-1/76)=2.9/38=9/19
Câu 4. Tính các tổng sau:
f) F = 1.2+2.3+3.4 +……..+ 2015.2016
g) G = 1.3+3.5+5.7 +……..+ 2015.2017
h) H = 1.4+4.7+7.10 +……..+ 2015.2018
i) I = 1+ 3+6 +……..+ 2031120
n) N = 1.3+2.4+3.5 +……..+ 1998.2000
m) M = 1.2.3+2.3.4+3.4.5 +……..+ 2015.2016.2017
n) N = 1.3.5+3.5.7+5.7.9 +……..+ 2013.2015.2017
A=1/2+ 1/6+1/12+...+1/132
B= 5/1.4+ 5/4.7+5/7.10+...+5/97.100
\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\)\(\frac{1}{132}\)= \(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{11\cdot12}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{11}-\frac{1}{12}\)\(=1-\frac{1}{12}=\frac{11}{12}\)
B = 5/1.4 + 5/4.7 + 5/7.10 + ... + 5/97.100
B = 5/3.(3/1.4 + 3/4.7 + 3/7.10 + ... + 3/97.100)
B = 5/3.(1 - 1/4 +1/4 -1/7 +1/7 - 1/10 + ... + 1/97 - 1/100)
B = 5/3.(1 - 1/100)
B = 5/3.99/100
B = 33/20
A=1/1.2+1/2.3+1/3.4+1/4.5+...+1/98.99+1/99.100
B=2/1.3+2/3.5+2/5.7+2/7.9+...+2/97.99+2/99.101
C=1/2+1/4+1/8+1/16+...+1/1024+1/2048
D=1/2+1/6+1/18+1/54+1/4374+1/13122 ( . (DẤU CHẤM LÀ ''NHÂN'')
\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\)
\(=1-\frac{1}{100}=\frac{99}{100}\)
\(B=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}+\frac{2}{99.101}\)
\(=1-\frac{1}{3}+\frac{!}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\)
\(=1-\frac{1}{101}=\frac{100}{101}\)
\(C=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+....+\frac{1}{1024}+\frac{1}{2048}\)
\(\Rightarrow\)\(2C=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+....+\frac{1}{512}+\frac{1}{1024}\)
\(\Rightarrow\)\(2C-C=\left(1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{1024}\right)-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{2048}\right)\)
\(\Leftrightarrow\)\(C=1-\frac{1}{2048}=\frac{2047}{2048}\)
Câu A bạn quên 1/4.5 kìa , với câu D đâu >>>
Tính tổng
a. 1/1.2 + 1/2.3 + 1/3.4 + ...+ 1/2015.2016
b. 2/1.3 + 2/3.5 + 2/5.7 + ...+ 2/99.101
c. 5/1.3 + 5/3.5 + 5/5.7 + ...+ 5/99.101
d. 1/2 + 1/6 + 1/12 + 1/20 + ...+ 1/9900
bn nào trả lời nhanh mik tích, cảm ơn ạ
còn cần không bạn, mk làm cho
Bài 1:Tính:
a,3 14/19 + 13/17 + 35/43 + 6 5/19 + 8/13
b,130 25/28 + 120 17/35
c,17 2/31 - (15/17 + 6 2/31)
d,(31 6/13 + 5 9/41) - 31 6/13
e,(17 24/31 - 3 7/8) - (2 38/31 - 4)
g,1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6
h,1/1.2 + 1/2.3 + 1/3.4 + .........+ 1/49.100
i,1/1.3 + 1/3.5 + 1/5.7 +........+ 1/97.99
Bài 2:Tìm 1 phân số có mẫu là 15 biết rằng giá trị của nó không thay đổi khi cộng tử với 2 và nhân mẫu với 2.
B= 1 trên 3.4 + 1 trên 4.5 + 1 trên 5. 6 + 1 trên 6.7 +1 trên 7.8
C= 1 trên 4.5 +1 trên 5.6 + 1 trên 6.7 + 1 trên 7.8 +1 trên 8.9
D= 2 3.5 + 2 5.7 + 2 7.9 + 2 9.11 +2 11.13
E = 3 1.4 + 3 4.7 + 3 7.10 + 3 10.13
Ta có: \(B=\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}\)
\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(=\frac{1}{3}-\frac{1}{8}\)
\(=\frac{5}{24}\)
Vậy \(B=\frac{5}{24}\)
Ta có: \(C=\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}\)
\(=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)
\(=\frac{1}{4}-\frac{1}{9}\)
\(=\frac{5}{36}\)
Vậy \(C=\frac{5}{36}\)
Ta có: \(C=\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot11}+\frac{2}{11\cdot13}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}\)
\(=\frac{1}{3}-\frac{1}{13}\)
\(=\frac{10}{39}\)
Vậy \(D=\frac{10}{39}\)