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Bài 2:
a, \(\dfrac{5}{23}\) \(\times\) \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) \(\times\) \(\dfrac{9}{26}\)
= \(\dfrac{5}{23}\) \(\times\) ( \(\dfrac{17}{26}\) + \(\dfrac{9}{26}\))
= \(\dfrac{5}{23}\) \(\times\) \(\dfrac{26}{26}\)
= \(\dfrac{5}{23}\)
b, \(\dfrac{3}{4}\) \(\times\) \(\dfrac{7}{9}\) + \(\dfrac{7}{4}\) \(\times\) \(\dfrac{3}{9}\)
= \(\dfrac{7}{12}\) + \(\dfrac{7}{12}\)
= \(\dfrac{14}{12}\)
= \(\dfrac{7}{6}\)
1. tìm x, y biết
a. 6/7:(x+3/5)-5/6=1/3
=> 6/7 :( x + 3/5 ) = 1/3 + 5/6
=> 6/7 : ( x + 3/5 ) = 2/6 + 5/6
=> 6/7 : ( x +3/5 ) = 7/6
=> x + 3/5 = 6/7 : 7/6
=> x + 3/5 = 6/7 . 6/7
=> x + 3/5 = 36/49
=> x = 36/49 -3/5
=> x = 33/245
b. (x-1/2) :3/5+2/3=7/9
=> ( x -1/2 ) : 3/5 = 7/9 -2/3
=> ( x -1/2 ) : 3/5 = 7/9 - 6/9
=> ( x -1/2 ) : 3/5 = 1/9
=> x -1/2 = 1/9 . 3/5
=> x -1/2 = 1/15
=> x = 1/15 + 1/2
=> x = 17/30
c. 11/10-3/5:x=2/5
=> 3/5 : x = 11/10 -2/5
=> 3/5 : x = 11/10 -4/10
=> 3/5 : x = 7/10
=> x = 3/5 : 7/10
=> x = 3/5 . 10/7
=> x = 6/7
.... Lười wá bạn làm tiếp đi!
các bạn ơi giải hộ mình với ai nhanh tất cả các bài mình tích cho
\(A=1+\frac{1}{2}+...+\frac{1}{16}\)
= \(1+\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\right)+\left(\frac{1}{5}+...+\frac{1}{8}\right)+\left(\frac{1}{9}+...+\frac{1}{12}\right)+\left(\frac{1}{13}+...+\frac{1}{16}\right)\)
> \(1+\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\right)+4\times\frac{1}{8}+4\times\frac{1}{12}+4\times\frac{1}{16}\)
=\(1+\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\right)+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\)
=\(1+2\times\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}\right)\)
= \(1+2\times\frac{13}{12}\)
= \(1+\frac{13}{6}\)
= \(1+2+\frac{1}{6}\)
= \(3+\frac{1}{6}\)>\(3\)
=> \(A>3+\frac{1}{6}>3\)
=> \(A>3+\frac{1}{6}>B\)
=> \(A>B\)
Không quy đồng mẫu số hãy so sánh các phân số sau :
a.19/20 và 20/21
b.17/21 và 23/27 3
c.1/29 và 45/43
a. 19/ 20= 1- 1/20
20/ 21= 1- 1/21
mà 1/20> 1/21 => 19/ 20< 20/ 21
b. 17/ 21= 1- 4/21
23/ 27= 1- 4/27
mà 4/21< 4/27 => 17/21< 23/27
c. 31/29= 1+ 2/29
45/43= 1+ 2/43
mà 2/29> 2/43 => 31/29> 45/43
a, 2015 - 2 × X = 101
2 x X = 2015 - 101
2 x X = 1914
X = 1914 : 2
X = 957
1a. 2015 - 2 x X = 101
2 x X = 2015 - 101
X = 1914 : 2
X = 957
b. 7 - (11 + X - 13) : \(2\frac{2}{3}\)= 2
(11 + X - 13) : \(2\frac{2}{3}\) = 7 - 2
11 + X - 13 = 5 x \(2\frac{2}{3}\)
11 + X = \(\frac{40}{3}\)+ 13
X = \(\frac{79}{3}\)- 11
X = \(\frac{46}{3}\)
c. 2012 - 5 x X = 17
5 x X = 2012 - 17
X = 1995 : 5
X = 399
d. \(5\frac{3}{4}\)+ (X - 2) x \(\frac{1}{3}\)= \(17\frac{3}{4}\)
(X - 2) x \(\frac{1}{3}\) = \(17\frac{3}{4}\)- \(5\frac{3}{4}\)
X - 2 = 12 : \(\frac{1}{3}\)
X = 36 + 2
X = 38
e. 12 x (X - 5) + 73 = 20
12 x (X - 5) = 20 - 73
X - 5 = -53 : 12
X = \(\frac{-53}{12}\)+ 5
X = \(\frac{7}{12}\)
1.
a) \(\frac{6}{15}+\frac{6}{35}+\frac{6}{63}+\frac{6}{99}+\frac{6}{143}\)
\(=\frac{6}{3.5}+\frac{6}{5.7}+\frac{6}{7.9}+\frac{6}{9.11}+\frac{6}{11.13}\)
\(=\frac{6}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{11}-\frac{1}{13}\right)\)
\(=\frac{6}{2}\left(\frac{1}{3}-\frac{1}{13}\right)\)
\(=\frac{6}{2}.\frac{10}{39}\)
\(=\frac{10}{13}\)
b) \(\frac{3}{24}+\frac{3}{48}+\frac{3}{80}+\frac{3}{120}+\frac{3}{168}\)
\(=\frac{3}{4.6}+\frac{3}{6.8}+\frac{3}{8.10}+\frac{3}{10.12}+\frac{3}{12.14}\)
\(=\frac{3}{2}\left(\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}-\frac{1}{10}+...+\frac{1}{12}-\frac{1}{14}\right)\)
\(=\frac{3}{2}.\left(\frac{1}{4}-\frac{1}{14}\right)\)
\(=\frac{3}{2}.\frac{5}{28}\)
\(=\frac{15}{56}\)
\(a.\frac{6}{3.5}+\frac{6}{5.7}+...+\frac{6}{11.13}\)
\(=3.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{13}\right)\)
\(=3.\left(\frac{1}{3}-\frac{1}{13}\right)\)
\(=3.\frac{10}{39}\)
\(=\frac{10}{13}\)