\(\frac{12.13+24.26+36.39}{24.26+48.52+72.78}\)
K
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CA
2
S
15 tháng 7 2018
a) \(9.11+32.9=9.\left(11+32\right)=9.43=387\)
b) \(23.25+12.23=23.\left(25+12\right)=23.37=851\)
c) \(12.13+24.26+36.39=12.13+12.2.13.2+12.3.13.3\)
\(=12.13+2^2\left(12.13\right)+3^2\left(12.13\right)\)
\(=12.13.\left(1+2^2+3^2\right)=12.13.14=2184\)
d) Câu này tương tự câu trên nha.
AT
0
EG
25 tháng 2 2018
a)
\(\frac{1\cdot2+2\cdot4+3\cdot6+4\cdot8+5\cdot10}{3\cdot4+6\cdot8+9\cdot12+12\cdot16+15\cdot20}\)
\(=\frac{1\cdot2\cdot\left(1+2\cdot2+3\cdot3+4\cdot4+5\cdot5\right)}{3\cdot4\cdot\left(1+2\cdot2+3\cdot3+4\cdot4+5\cdot5\right)}\)
\(=\frac{1\cdot2}{3\cdot4}=\frac{1}{6}\)
b) \(\frac{12\cdot13+24\cdot26+36\cdot39}{24\cdot26+48\cdot52+72\cdot78}\)
\(=\frac{12\cdot13\cdot\left(1+2\cdot2+3\cdot3\right)}{24\cdot26\cdot\left(1+2\cdot2+3\cdot3\right)}\)
\(=\frac{12\cdot13}{24\cdot26}=\frac{1}{4}\)
\(\frac{2\cdot3+4\cdot6+14\cdot21}{3\cdot5+6\cdot10+21\cdot35}=\frac{2\cdot3\cdot\left(1+2\cdot2+7\cdot7\right)}{3\cdot5\cdot\left(1+2\cdot2+7\cdot7\right)}=\frac{2\cdot3}{3\cdot5}=\frac{2}{5}\)
NK
1
MN
20 tháng 9 2021
24.26. It is very ______________ to go around the city centre by bike.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
25.27. It is ______________ for you to take cycling as a type of exercise because it brings many benefits.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
26.28. It is ______________ to cycle your bike along a road on the coast of Nha Trang, breathing fresh air and enjoying the salty taste of the sea.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
27.29. The boy was too ______________ to speak. He became breathless.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
28.30. They were ______________ to get a place in the kindergarten for their small girl because they couldn't get the application form.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
29.31. It is ______________ for parents to have a lot of children at present.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
30.32. It is not ______________ to cook a lot of food for Tet because we can have good food all year round.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
31.33. Everyone was ______________ to go to the market on a day near Tet.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
32.34. Fifty years ago, we had very few schools and the rows of classrooms looked like ______________ houses.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
33.35. During wartime, all around the rows of classrooms there were ______________ so that children could shelter from bombs.
(1 Điểm)
A. nervous
B. eager
C. practical
D. trenches
E. necessary
F. difficult
G. good
H. hopeless
I. thatched
J. romantic
26 tháng 5 2021
2/20x22 + 2/22x24 + 2/24x26 +...+2/78x80
=2 x(1/20x22 + 1/22x24 + 1/24x26 +...+1/78x80)
=2 x(1/20 - 1/22 + 1/22 -....+1/78 - 1/80)
=2 x (1/20 - 1/80)
=2 x 3/80
=3/40
Vì 3/40 < 1/9 nên 2/20x22 + 2/22x24 + 2/24x26 +...+2/78x80 < 1/9
VP
3
T
17 tháng 3 2018
Đề sai. Sửa đề: Ta có: \(B=\frac{5}{40.44}+\frac{5}{44.48}+\frac{5}{48.52}+...+\frac{5}{76.80}+\frac{5}{2011}\)
\(=\left(\frac{5}{40.44}+\frac{5}{44.48}+\frac{5}{48.52}+...+\frac{5}{76.80}\right)+\frac{5}{2011}\)
\(=\frac{5}{4}\left(\frac{1}{40.44}+\frac{1}{44.48}+\frac{1}{48.52}+..+\frac{1}{76.80}\right)+\frac{5}{2011}\)
\(=\frac{5}{4}\left(\frac{1}{40}-\frac{1}{44}+\frac{1}{44}-\frac{1}{48}+\frac{1}{48}-\frac{1}{52}+...+\frac{1}{76}-\frac{1}{80}\right)+\frac{5}{2011}\)
\(=\frac{5}{4}\left(\frac{1}{40}-\frac{1}{80}\right)+\frac{5}{2011}=\frac{5}{4}.\frac{1}{80}+\frac{5}{2011}=\frac{1}{64}+\frac{5}{2011}\)
LK
17 tháng 3 2018
bạn CTV tth làm sai rồi nhé
\(\frac{5}{40.44}+\frac{5}{44.48}+...+\frac{5}{76.80}+\frac{5}{2011}\)
\(=\frac{5}{4}\left(\frac{4}{40.44}+\frac{4}{44.48}+...+\frac{4}{76.80}\right)+\frac{5}{2011}\)
\(=\frac{5}{4}\left(\frac{1}{40}-\frac{1}{44}+\frac{1}{44}-...-\frac{1}{76}+\frac{1}{76}-\frac{1}{80}\right)+\frac{5}{2011}\)
\(=\frac{5}{4}\left(\frac{1}{40}-\frac{1}{80}\right)+\frac{5}{2011}=\frac{5}{4}.\frac{1}{80}+\frac{5}{2011}\)
\(=\frac{1}{64}+\frac{5}{2001}\)
Đặt tử số là A , mẫu số là B
Ta có : B = 24 . 26 + 48 . 52 + 72 . 78
= ( 12 . 2 ) . ( 13 . 2 ) + ( 24 . 2 ) . ( 26 . 2 ) + ( 36 . 2 ) . ( 39 . 2 )
= ( 12 .13 ) . ( 2. 2 ) + ( 24 . 26 ) . ( 2 . 2 ) + ( 36 . 39 ) . ( 2 . 2 )
= ( 12 . 13 ) . 4 + ( 24 . 26 ) . 4 + ( 36 . 39 ) . 4
= 4 . ( 12 . 13 + 24 . 26 + 36 . 39 )
= 4 . A ( A là tử số )
lại có : A/B = A/4A
= 1/4
Chúc học giỏi
167/728