128 x 72 + 14 x 256 -56
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
128x72+14x256
=128x72+14x2x128
=128x72+28x128
=128x(72+28)
=128x100
=12800
![](https://rs.olm.vn/images/avt/0.png?1311)
1) 1/1.2 + 1/2.3 + ... + 1/6.7
= 1 - 1/2 + 1/2 - 1/3 + ... + 1/6 - 1/7
= 1 - 1/7
= 6/7
2) 1/2 + 1/6 + 1/12 + .. + 1/72
= 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/8.9
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/8 - 1/9
= 1 - 1/9
= 8/9
3) \(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right)...\left(1-\frac{1}{2019}\right)\)
= \(\frac{1}{2}.\frac{2}{3}...\frac{2019}{2020}\)
= \(\frac{1.2....2019}{2.3...2020}\)
= \(\frac{1}{2020}\)
4) A = \(\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+...+\frac{1}{512}\)
= \(\frac{1}{2^2}+\frac{2}{2^3}+\frac{1}{2^4}+...+\frac{1}{2^9}\)
=> 2A = \(\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^8}\)
Lấy 2A - A = \(\left(\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^8}\right)-\left(\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+...+\frac{1}{2^9}\right)\)
A = \(\frac{1}{2}-\frac{1}{2^9}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=0,36x350+1,2x20x3+36x4,5\)
\(A=0,36x3,5x100+1,2x2x10x3+36x4,5\)
\(A=36x3,5+36x2+36x4,5\)
\(A=36x\left(3,5+4,5+2\right)\)
\(A=36x10=360\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 1: \(\frac{17}{51}\)x \(\frac{45}{30}\)= \(\frac{1}{3}\)x \(\frac{3}{2}\)
= \(\frac{1}{2}\).
Câu 2: \(\frac{24}{15}\)x \(\frac{56}{72}\)x \(\frac{10}{14}\)= \(\frac{8}{5}\)x \(\frac{7}{9}\)x \(\frac{5}{7}\)
= \(\frac{56}{45}\)x \(\frac{5}{7}\)
= \(\frac{8}{9}\)
Câu 3: \(\frac{32}{48}\times\frac{35}{21}\times\frac{63}{14}\times\frac{9}{30}=\frac{2}{3}\times\frac{5}{3}\times\frac{9}{2}\times\frac{3}{10}=\frac{3}{2}\)
k nha
a)17/51x45/40=1/3x3/2=3/6=1/2
b)24/15x56/72x10/14=8/5x7/9x5/7=8/9
c)32/48x35/21x63/14x9/30=2/3x5/3x9/2x3/10=3/2
![](https://rs.olm.vn/images/avt/0.png?1311)
256 x 6=512 x 3
512 x 3=256 x 6
999 x 2>1000
512 x 5>1024
1024<512 x 5
1024=512 x 2
512=256 x 2
256=128 x 2
128=64 x 2
64=32 x 2
32=16 x 2
![](https://rs.olm.vn/images/avt/0.png?1311)
a/=256x(82+18)
=256x100
=25600
b/211x(56+43+1)
=211x100=21100
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1: Đặt tính rồi tính :
23,45 x 8,2 = 192,29
37,9 x 3,04 = 115,216
56,2 x 1,003 = 56,3686
72,4 x 3,05 = 220,82
Bài 5: Tính nhanh:
23,14 x 56 + 44 x 23,14
= 23,14 x (56 + 44)
= 23,14 x 100
= 2314
12,25 x 109 – 9 x 12,25
= 12,25 x (109 - 9)
= 12,25 x 100
= 1225
2,75 x 36 – 14 x 2,75 + 2,75 x 78
= 2,75 x (36 - 14 + 78)
= 2,75 x 100
= 275
1,56 x 67 + 34 x 1,56 – 1,56
= 1,56 x (67 + 34) - 1,56
= 1,56 x 101 - 1,56
= 157,56 - 1,56
= 156
![](https://rs.olm.vn/images/avt/0.png?1311)
a, (-72).(15 - 49) + 15.(-56 + 72)
= -72 . 15 + 72.49 - 15.56 + 15.72
= (-72.15 + 15.72) + (72.49 - 15.56)
= 3528 - 84
= 2688
1b, 1532 + (-186) + (-1432) + (-14) + 123
= (1532 - 1432) - (186 + 14) + 123
= 100 - 200 + 123
= 223 - 200
= 23
BẰNG 12744
128 x 72 + 14 x 128 x 2 - 56
= 128(72 + 14 x 2) -56
= 128 x