a, (x- \(\dfrac{2}{7}\))(x+\(\dfrac{3}{4}\))

⇔ \(\left[{}\begin{matrix}x-\dfrac{2}{7}=0\\x+\dfrac{3}{4}=0\end{matrix}\right.\)

⇔ \(\left[{}\begin{matrix}x=\dfrac{2}{7}\\x=-\dfrac{3}{4}\end{matrix}\right.\)

b, \(\dfrac{2}{3}\) x - \(\dfrac{2}{5}\) = \(\dfrac{1}{2}\) x - \(\dfrac{1}{3}\)

⇔ \(\dfrac{2}{3}\) x - \(\dfrac{1}{2}\) x = \(\dfrac{2}{5}\) -  \(\dfrac{1}{3}\) 

⇔ \(\dfrac{x}{6}\) = \(\dfrac{1}{15}\)

⇔ x = \(\dfrac{1}{15}\) x 6 

     x = \(\dfrac{2}{5}\)

c, \(\dfrac{1}{3}\) x + \(\dfrac{2}{5}\) (x+1)= 0

⇔ \(\dfrac{5x+6x+6}{15}\) = 0

⇔ 11x + 6 = 0

⇔ x = - \(\dfrac{6}{11}\)

tìm x

a, (x - 2/7 ) ( x + 3/4 )=0

<=> x - 2/7= 0 hoặc x+3/4 = 0
=> X = 2/7 hoặc x = -3/4

c,1/3x +2/5 (x+1 )=0

=> 1/3x + 2/5x + 2/5.1 = 0

=> x.(1/3 + 2/5 ) +2/5 = 0

=> x.11/15 + 2/5 = 0

=> x.11/15 = 0 - 2/5

=> x.11/15 = -2/5

=> x = -2/5 : 11/15

=> x = -6/11

Vậy x = -6/11

\(\dfrac{1}{6}\) - 0,4 . \(\dfrac{5}{8}\) + \(\dfrac{1}{2}\)

= \(\dfrac{1}{6}\) - \(\dfrac{1}{4}\) + \(\dfrac{1}{2}\)

= \(\dfrac{2}{12}\) - \(\dfrac{3}{12}\) + \(\dfrac{6}{12}\)

= \(\dfrac{5}{12}\)

1/6-0,4.5/8+1/2

=1/6-1/4+1/2

=2/12-3/12+6/12

=5/12

= (16/3 - 4.5/3) . (17/3 - 4.5/3) (30/3 - 4.5/3)

= (16/3 - 20/3) . (17/3 - 20/3) (30/3 - 20/3)

= -4/3 . -3/3 . 10/3

= 4/3 - 10/3

= -2

Đề vẫn giải được nhưng số khá xấu, không phù hợp với lớp 7. Bạn xem lại xem đã đúng đề chưa vậy>

\(\dfrac{-19}{2}\) < a < \(\dfrac{-20}{3}\)

- \(\dfrac{57}{6}\) < a < \(\dfrac{-40}{6}\)

a = - 56/6; -55/6; -54/6; - 53/6; - 52/6; - 51/6; ......; -42/6; -41/6

b, \(\dfrac{1}{3}\) < \(\dfrac{4}{b}\) < \(\dfrac{1}{2}\) 

\(\dfrac{4}{12}\) < \(\dfrac{4}{b}\)< \(\dfrac{4}{8}\)

b = 11; 10; 9 

2(x-3)+3(x+1)=4x-1

=>2x-6+3x+3=4x-1

=> 2x+3x-4x=-1+6-3

=> x(2+3-4)=2

=>x=2

Vậy x=2

\(2\times\left(x-3\right)+3\times\left(x+1\right)=4x-1\)

\(2x-6+3x+3=4x-1\)

\(\Rightarrow2x-6+3x+3-\left(4x-1\right)=0\)

\(2x-6+3x+3-4x+1=0\)

\(2x+3x-4x-6+3+1=0\)

\(\left(2+3-4\right)x-\left(6-3-1\right)=0\)

\(x-2=0\)

\(x=0+2\)

\(x=2\)

2(x-3)+3(x+1)=4x-1

=>2x-6+3x+3=4x-1

=> 2x+3x-4x=-1+6-3

=> x(2+3-4)=2

=>x=2

Vậy x=2