y x 2/5 =8/21

y= 8/21:2/5

y= 20/21

12/7: y =7/5-2/5

12/7:y = 1

y = 12/7 :1

y= 12/7

\(y\times\dfrac{2}{5}=\dfrac{8}{21}\\ y=\dfrac{8}{21}:\dfrac{2}{5}\\ y=\dfrac{20}{21}\\ \dfrac{12}{7}:y+\dfrac{2}{5}=\dfrac{7}{5}\\ \dfrac{12}{7}:y=\dfrac{7}{5}-\dfrac{2}{5}\\ \dfrac{12}{7}:y=1\\ y=\dfrac{12}{7}:1=\dfrac{12}{7}\)

y=(4/7:3/2):2/5

y=20/21

\(x=\dfrac{7}{25}+\dfrac{-1}{5}=\dfrac{7}{25}-\dfrac{1}{5}=\dfrac{2}{25}.\\ x=\dfrac{5}{11}+\dfrac{4}{-9}=\dfrac{5}{11}-\dfrac{4}{9}=\dfrac{1}{99}.\\ \dfrac{5}{9}-\dfrac{x}{-1}=\dfrac{-1}{3}\Leftrightarrow\dfrac{5}{9}+x=-\dfrac{1}{3}.\Leftrightarrow x=-\dfrac{8}{9}.\)

\(x=\dfrac{7}{25}+-\dfrac{1}{5}=>\dfrac{7}{25}+-\dfrac{5}{25}=>x=\dfrac{2}{25}\)

\(x=\dfrac{5}{11}+\dfrac{4}{-9}=>\dfrac{-45}{-99}+\dfrac{44}{-99}=>x=\dfrac{-1}{-99}=\dfrac{1}{99}\)

\(\dfrac{5}{9}-\dfrac{x}{-1}=-\dfrac{1}{3}=>-\dfrac{1}{3}-\dfrac{5}{9}=>\dfrac{x}{-1}=-\dfrac{8}{9}=>x=-\dfrac{8}{9}\)

\(x=\dfrac{7}{25}+\dfrac{-1}{5}\\ \Rightarrow x=\dfrac{7}{25}+\dfrac{-5}{25}\\ \Rightarrow x=\dfrac{2}{25}\\ x=\dfrac{5}{11}+\dfrac{4}{-9}\\ \Rightarrow x=\dfrac{-45}{-99}+\dfrac{44}{-99}\\ \Rightarrow x=\dfrac{45}{99}+\dfrac{44}{99}\\ \Rightarrow x=\dfrac{95}{99}\\ \dfrac{5}{9}-\dfrac{x}{-1}=\dfrac{-1}{3}\\ \Rightarrow\dfrac{x}{-1}=\dfrac{5}{9}-\dfrac{-1}{3}\\ \Rightarrow\dfrac{x}{-1}=\dfrac{5}{9}-\dfrac{-3}{9}\\ \Rightarrow\dfrac{x}{-1}=\dfrac{8}{9}\Rightarrow x\cdot9=-1\cdot8=-8\\ \Rightarrow x\cdot9=-8\\ \Rightarrow x=\dfrac{-8}{9}\)

\(\Leftrightarrow xy=63\)

\(\Leftrightarrow\left(x,y\right)\in\left\{\left(1;63\right);\left(3;21\right);\left(7;9\right);\left(-63;-1\right);\left(-21;-3\right);\left(-9;-7\right)\right\}\)

1> a) \(\frac{5}{7}x4:\frac{5}{9}=\frac{5}{7}:\frac{5}{9}x4=\frac{5}{7}x\frac{9}{5}x4=\frac{9}{7}x4=\frac{9x4}{7}=\frac{36}{7}\)

\(b,8x\frac{2}{3}:\frac{1}{2}=8x\frac{2}{3}x\frac{2}{1}=8x2x\frac{2}{3}=16x\frac{2}{3}=\frac{32}{3}\)

\(c,6:\frac{3}{5}-\frac{7}{6}x\frac{6}{7}=6x\frac{5}{3}-1=10-1=9\)

\(\frac{21}{5}x\frac{10}{11}+\frac{57}{11}=\frac{42}{11}+\frac{57}{11}=\frac{99}{11}=9\)

2) a) \(\frac{35}{9}:x=\frac{35}{6}\)

\(x=\frac{35}{9}:\frac{35}{6}\)

\(x=\frac{35}{9}x\frac{6}{35}\)

\(x=\frac{2}{3}\)

b) \(\left(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+\frac{1}{5x6}\right)x10-X=0\)

\(\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{5}-\frac{1}{6}\right)x10-X=0\)

\(\left(\frac{1}{1}-\frac{1}{6}\right)x10-X=10\)

\(\frac{5}{6}x10-X=0\)

\(X=\frac{5}{6}x10=\frac{25}{3}\)

Đúng nha !!!!

1/a/\(\frac{5}{7}\cdot4:\frac{5}{9}=\frac{20}{7}:\frac{5}{9}=\frac{20}{7}\cdot\frac{9}{5}=\frac{36}{7}\)

b/\(8\cdot\frac{2}{3}:\frac{1}{2}=\frac{16}{3}:\frac{1}{2}=\frac{16}{3}\cdot\frac{2}{1}=\frac{32}{3}\)

c/\(6:\frac{3}{5}-\frac{7}{6}\cdot\frac{6}{7}=6\cdot\frac{5}{3}-1=10-1=9\)

2/a/\(\frac{35}{9}:x=\frac{35}{6}\)

\(x=\frac{35}{9}:\frac{35}{6}=\frac{35}{9}\cdot\frac{6}{35}\)

\(x=\frac{2}{3}\)

b/\(\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}\right)\cdot10-x=0\)

\(\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\right)\cdot10-x=0\)

\(\left(\frac{30}{60}+\frac{10}{60}+\frac{5}{60}+\frac{2}{30}\right)\cdot10-x=0\)

\(\frac{47}{60}\cdot10-x=0\)

\(\frac{47}{6}-x=0\)

\(x=\frac{47}{6}-0\)

\(x=\frac{47}{6}\)

xs

BT1 :thực hành phép tính

4/3+-11/31+3/10-20/31-2/5 = 7/30

7/12-1/-16+3/4 = 67/48

2/11.-5/4+-9/11.5/4+ 1 và 3/4 = -1/4 * và 3/4 là sao bạn *

-9/27-25/75 = -2/3

\(\left(19\frac{5}{8}:\frac{7}{12}-13\frac{1}{4}:\frac{7}{12}\right).\frac{4}{5}\)

\(=\left(\frac{157}{8}:\frac{7}{12}-\frac{53}{4}:\frac{7}{12}\right).\frac{4}{5}\)

\(=\left[\left(\frac{157}{8}-\frac{53}{4}\right):\frac{7}{12}\right].\frac{4}{5}\)

\(=\left[\frac{51}{8}:\frac{7}{12}\right].\frac{4}{5}\)

\(=\frac{153}{14}.\frac{4}{5}\)

\(=\frac{306}{35}\)

\(\left(\frac{-2}{5}+\frac{3}{7}\right)-\left(\frac{4}{9}+\frac{12}{20}-\frac{13}{35}\right)+\frac{7}{35}\)

\(=\frac{1}{35}-\frac{212}{315}+\frac{7}{35}\)

\(=\frac{1}{35}+\frac{-212}{315}+\frac{7}{35}\)

\(=\frac{9}{315}+\frac{-212}{315}+\frac{63}{315}\)

\(=\frac{-140}{315}=\frac{-4}{9}\)

\(\left(4\frac{5}{57}-3\frac{4}{51}+8\frac{13}{29}\right)-\left(3\frac{5}{57}-6\frac{16}{29}\right)\)

\(=\left(\frac{233}{57}-\frac{157}{51}+\frac{245}{29}\right)-\left(\frac{176}{57}-\frac{190}{29}\right)\)

\(=\frac{1941}{323}-\frac{-5726}{1653}\)

\(=\frac{14011}{1479}\)

\(\text{#ID07 - DNfil}\)

`A = -(x + 1)^2 + 5`

Ta có: `(x + 1)^2 \ge 0` `AA` `x`

`=> -(x + 1)^2 \le 0` `AA` `x`

`=> -(x + 1)^2 + 5 \le 5` `AA` `x`

Vậy, GTLN của A là `5` khi `(x + 1)^2 = 0 => x + 1 = 0 => x = -1`

________

2.

`2x - 0,7 = 1,3`

`=> 2x = 1,3 + 0,7`

`=> 2x = 2`

`=> x = 1`

Vậy, `x = 1`

__

`x - \sqrt{25} = (2/5 - 6/5)`

`=> x - \sqrt{25} = -3/5`

`=> x = -3/5 + \sqrt{25}`

`=> x = -3/5 + 5`

`=> x = 22/5`

Vậy, `x = 22/5`

__

`3/4 + 1/4 \div x = 2/5`

`=> 1/4 \div x = 2/5 - 3/4`

`=> 1/4 \div x = -7/20`

`=> x = 1/4 \div (-7/20)`

`=> x = -5/7`

Vậy, `x = -5/7.`

\(1)\frac{12}{7}\times \frac{7}{4}+\frac{35}{11}:\frac{245}{121}\)

\(=3+\frac{35}{11}\times \frac{121}{245}\)

\(=3+\frac{11}{7}\)

\(= 3\frac{1}{7}(=\frac{22}{7})\)

ms cs 1 câu nên mk chưa cho k đâu

Bài 1

= \(\frac{22}{7}\)

bài 3

x = 4

y = 3

k mik nhé