Bài 1: Mở rộng khái niệm phân số

12/25<16/31

thankss

[x-1]/7=[-3]/[y+3]`

`=>(x-1)(y+3)=-21=-21.1=-1.21=-3.7=-7.3`

`@{(x-1=-21),(y+3=1):}=>{(x=-20),(y=-2):}`

`@{(x-1=-1),(y+3=21):}=>{(x=0),(y=18):}`

`@{(x-1=-3),(y+3=7):}=>{(x=-2),(y=4):}`

`@{(x-1=-7),(y+3=3):}=>{(x=-6),(y=0):}`

a: x=3*2/1=6

b: x=3/(-5)*(-2)=6/5

c: =>x+1=3/2

=>x=1/2

d: =>x+2=4

=>x=2

e: =>x+5=56/9

=>x=56/9-5=56/9-45/9=11/9

\(a,\dfrac{1}{2}=\dfrac{3}{x}\\ \dfrac{3}{6}=\dfrac{3}{x}\\ x=6\\ b,\dfrac{x}{-2}=\dfrac{3}{-5}\\\dfrac{\left(-5\right).x}{10}=\dfrac{-6}{10}\\ -5.x=-6\\ x=-6:\left(-5\right)\\ x=\dfrac{6}{5}\\ c,\dfrac{x+1}{2}=\dfrac{3}{4}\\ \dfrac{\left(x+1\right).2}{4}=\dfrac{3}{4}\\ \left(x+1\right).2=3\\ x+1=3:2\\ x+1=1,5\\ x=1,5-1\\ x=0,5\\ d,\dfrac{8}{x+5}=\dfrac{9}{7}\\ 8.7=9.\left(x+5\right)\\ 56=9.\left(x+5\right)\\ x+5=56:9\\ x+5=\dfrac{56}{9}\\ x=\dfrac{56}{9}-5\\ x=\dfrac{11}{9} \)

Lời giải:
Tính thêm lề thì diện tích kính phủ tranh là:
$(32+9+9)\times (42+9+9)=3000$ (cm²)

Đổi $3000$ cm² = $0,3$ m²

Tấm kính giá: $0,3\times 180000=54000$ (đồng)

`x . 3/7 = 2/3`

`=>x= 2/3 : 3/7`

`=>x= 2/3 . 7/3`

`=>x=14/9`

`-----------`

`x : 8/11 = 11/3`

`=>x= 11/3 . 8/11`

`=>x= 88/33`

`=>x=8/3`

`-----------`

`4/7 . x - 2/3 = 1/5`

`=> 4/7 . x = 1/5 +2/3`

`=>4/7 . x =3/15 + 10/15`

`=>4/7 . x =13/15`

`=>x= 13/15 : 4/7`

`=>x= 13/15 xx 7/4`

`=>x= 91/60`

Lời giải:

$x.\frac{3}{7}=\frac{2}{3}$

$x=\frac{2}{3}: \frac{3}{7}=\frac{14}{9}$

-----------

$x: \frac{8}{11}=\frac{11}{3}$

$x=\frac{11}{3}.\frac{8}{11}=\frac{8}{3}$

-----------

$\frac{4}{7}x-\frac{2}{3}=\frac{1}{5}$

$\frac{4}{7}x=\frac{2}{3}+\frac{1}{5}=\frac{13}{15}$

$x=\frac{13}{15}: \frac{4}{7}=\frac{91}{60}$

x × 3/7 = 2/3 

          x = 2/3 ÷ 3/7 

          x = 14/9 

x ÷ 8/11 = 11/3 

             x = 11/3 × 8/11 

             x = 8/3 

4/7 × x - 2/3 = 1/5 

4/7 × x.         = 1/5 + 2/3 

4/7 × x.         = 13/15 

           x.        = 13/15 ÷ 4/7 

           x.        = 91/60

\(\Leftrightarrow-\dfrac{2}{9}+\dfrac{2}{3}-\dfrac{4}{9}>=x>=\dfrac{3}{7}-\dfrac{7}{5}+\dfrac{11}{7}+\dfrac{2}{5}\)

=>0>=x>=1

=>\(x\in\varnothing\)

Lời giải:
a.

$-18: \frac{3}{5}=-18.\frac{5}{3}=-30$

b.

$\frac{3}{4}:(-9)=\frac{3}{4}.\frac{-1}{9}=\frac{-1}{12}$

c.

$\frac{13}{20}-\frac{6}{7}: \frac{10}{21}=\frac{13}{20}-\frac{6}{7}.\frac{21}{10}$

$=\frac{13}{20}-\frac{9}{5}=\frac{13}{20}-\frac{36}{20}=\frac{-23}{20}$

d.

$\frac{-21}{5}: (\frac{7}{3}.\frac{7}{5})=\frac{-21}{5}: \frac{49}{15}$

$=\frac{-21}{5}.\frac{15}{49}=\frac{-9}{7}$

e.

$(\frac{-2}{5}+\frac{1}{4}): (1-\frac{2}{5})$

$=\frac{-3}{20}: \frac{3}{5}=\frac{-1}{4}$

\(8:\left(-3\right)=\dfrac{8}{-3}=\dfrac{-8}{3}\)

`1654 m^2 = 1654 : 10000 = 0,1654` `ha`

`6,5` `km^2` `=` `6,5 xx 100 = 650` `ha`

`12,44` `m` `=` `12` `m` `44` `cm`

Sửa đề: 25%*x=-4/3

=>1/4x=-4/3

=>x=-4/3*4=-16/3