Question

Câu 9. (2 điểm) Tìm số hữu tỉ $x$ trong các tỉ lệ thức sau:

a) $\dfrac x{-3} = \dfrac74$;

b) $\dfrac{x + 9}{15 - x} = \dfrac23$.

Answer 1

a, \(\dfrac{x}{-3}\)= \(\dfrac{7}{4}\) ⇒ x = \(\dfrac{7}{4}\)x (-3) ⇒ x = - \(\dfrac{21}{4}\)

b, \(\dfrac{x+9}{15-x}\) = \(\dfrac{2}{3}\)  ⇒ 3(x+9)  = 2( 15-x) ⇒ 3x + 27 = 30 - 2x

⇒ 3x + 2x = 30 - 27 ⇒

 5x = 3 ⇒ x = 3 : 5 ⇒ x = \(\dfrac{3}{5}\)

 

 

Answer 2

Xãa â

Answer 3

a) x=7.(-3):4

x= (-21):4

x= -5.25

Answer 4

a, x/3=7/4

x=7.(-3)/4

x=-21/4

b,x+9/15-x=2/3

(15-x).2=3x+27

30-2x=3x+27

5x=3

x=3/5

Answer 5

9a) x= -21/4

b) x=3/5

 

Answer 6

a.  x = ( -3 ) x 7 : 4 = ( -5,25 )

b.  ( x + 9 ) =  9 x 3 : 2 = 13,5

     ( 15 - x ) = 15 x 2 :3 = 10

Answer 7

a) 7.-3=x.4

=>(7.-3):4

=>-21/4

Answer 8

a

Answer 9

a) x= -5,25

b)x= \(\dfrac{3}{5}\)

Answer 10

a\()\)x\(=\)\((\)-3x7\()\)\(\div\)4 

x\(=\)-21​\(\div\)4​

x​​

 

Answer 11

a) từ tỉ lệ thức trên ta có : \(x=\dfrac{-3.7}{4}=\dfrac{-21}{4}\)

b)(15-x).2= (x+9).3

30 - 2x = 3x + 27

5x = 3

x = \(\dfrac{3}{5}\)

 

Answer 12

4x=(-3).7

4x=-21        x=(-21):4     x=-5,25

 

 

Answer 13

a) x−3=74−3x​=47​

x=7.(−3)4x=47.(−3)​

x=−214x=4−21​.

b) x+915−x=2315−xx+9​=32​

$(15-x).2=(x+9).3$

$30-2x=3x+27$

$5x=3$

x=35x=53​.

 

Answer 14

a) X=-3.7:4=-5,25   b)

Answer 15

a) -28/3

b) x+9/15-x=(9+3)+9/15-(-3)

Answer 16

a) -28/3

b) x+9/15-x=(9+3)+9/15-(-3)

Answer 17

Answer 18

a, \(\dfrac{x}{-3}\) = \(\dfrac{7}{4}\)

⇒ x.4 = -3.7

⇒ x =\(\dfrac{-3.7}{4}\)

⇒ x = \(\dfrac{-21}{4}\)

b, \(\dfrac{x+9}{15-x}\) = \(\dfrac{2}{3}\)

⇒ ( x + 9 ).3 = ( 15 - x ).2

⇒ 3x + 27 = 30 - 2x

⇒ 3x + 2x = 30 - 27

⇒ 5x = 3

⇒ x = \(\dfrac{3}{5}\)