Question

[Nguyễn Thi An Na]

TÌM X, BIẾT

A)\(\frac{-3}{X}=\frac{15}{7}\)

B)\(\frac{X+3}{4}=\frac{5}{20}\)

C)\(\frac{1,2}{30}=\frac{3X+4}{50}\)

d)\(\frac{X-1}{3}=\frac{X+1}{5}\)

Answer 1

[nameless]

a) \(-\frac{3}{x}=\frac{15}{7}\)
=> -3.7 = 15x
=> 15x = -21
=>     x = -21:15
=>     x = -1,4
Vậy x = -1,4
b) \(\frac{x+3}{4}=\frac{5}{20}\)
\(\Rightarrow\frac{x+3}{4}=\frac{1}{4}\)
=> x + 3 = 1
=> x       = 1 - 3
=> x       = -2 
Vậy x = -2
d) \(\frac{x-1}{3}=\frac{x+1}{5}\)
=> 5(x - 1) = 3(x + 1)
=> 5x - 5   = 3x + 3
=> 5x - 3x = 5 + 3
=> 2x        = 8
=>   x        = 8:2
=>   x        = 4
Vậy x = 4

Answer 2

[Huỳnh Quang Sang]

\(a,\frac{-3}{x}=\frac{15}{7}\)

=> -21 = 15x

=> \(x=-\frac{21}{15}=-\frac{7}{5}\)

b, 

\(\frac{x+3}{4}=\frac{5}{20}\)

=> \(\frac{5(x+3)}{20}=\frac{5}{20}\)

=> 5\((x+3)\)= 5

=> x + 3 = 1

=> x = -2

\(c,\frac{1,2}{30}=\frac{3x+4}{50}\)

=> \(\frac{\frac{12}{10}}{30}=\frac{3x+4}{50}\)

=> \(\frac{\frac{6}{5}}{30}=\frac{3x+4}{50}\)

=> \(\frac{2}{50}=\frac{3x+4}{50}\)

=> 3x + 4 = 2

=> 3x = -2

=> x = -2/3

\(d,\frac{x-1}{3}=\frac{x+1}{5}\)

=> 5[x - 1] = 3[x + 1]

=> 5x - 5 = 3x + 3 

=> 5x - 5 - 3x = 3

=> 5x - 3x - 5 = 3

=> 2x = 8

=> x = 4