Em đăng câu hỏi `1.9` sang câu khác nhé^^
`a, x/3 =7/9`
`=> 9x=3.7`
`=> 9x=21`
`=>x= 21/9`
`=> x= 7/3`
__
`b, 8/x = 5/35`
`=> 8/x = 1/7`
`=> x=8.7`
`=> x= 56`
__
`c,(2x-5)/39 = 6/27`
`=> (2x-5).27=6.39`
`=> (2x-5).27=234`
`=> 2x-5= 234:27`
`=>2x-5=26/3`
`=> 2x= 26/3 +5`
`=>2x=41/3`
`=>x=41/3 : 2`
`=>x=41/6`
__
`d,(x+3)/13 = 7/39`
`=> (x+3).39 = 7.13`
`=> (x+3).39=91`
`=> x+3=91:39`
`=>x+3=7/3`
`=>x=7/3-3`
`=>x=-2/3`
Bài 1.8:
a) \(\dfrac{x}{3}=\dfrac{7}{9}\)
\(\Rightarrow x=\dfrac{7\cdot3}{9}\)
\(\Rightarrow x=\dfrac{7}{3}\)
b) \(\dfrac{8}{x}=\dfrac{5}{35}\) (x khác 0)
\(\Rightarrow x=\dfrac{8\cdot35}{5}\)
\(\Rightarrow x=56\)
c) \(\dfrac{2x-5}{39}=\dfrac{6}{27}\)
\(\Rightarrow2x-5=\dfrac{39\cdot6}{27}\)
\(\Rightarrow2x-5=\dfrac{26}{3}\)
\(\Rightarrow2x=\dfrac{41}{3}\)
\(\Rightarrow x=\dfrac{41}{6}\)
d) \(\dfrac{x+3}{13}=\dfrac{7}{39}\)
\(\Rightarrow x+3=\dfrac{7\cdot13}{39}\)
\(\Rightarrow x+3=\dfrac{7}{3}\)
\(\Rightarrow x=\dfrac{7}{3}-3\)
\(\Rightarrow x=-\dfrac{2}{3}\)
Bài 1.9
a) 2x/9 = 96/27
2x.27 = 96.9
54x = 864
x = 864 : 54
x = 16
b) 3/16 = x/8
16.x = 3.8
16.x = 24
x = 24 : 16
x = 3/2
c) 85/(3x + 2) = 75/35
(3x + 2).75 = 85.35
(3x + 2).75 = 2975
3x + 2 = 2975 : 75
3x + 2 = 119/3
3x = 119/3 - 2
3x = 113/3
x = 113/3 : 3
x = 113/9
d) 32/16 = (5x - 7)/8
(5x - 7)/8 = 32
5x - 7 = 32.8
5x - 7 = 256
5x - 7 = 256 + 7
5x = 263
x = 263/5
