Question

Answer 1

Bài 2:

a, \(5x\left(4x-7\right)-10x\left(2x+3\right)=65\)

\(\Leftrightarrow20x^2-35x-20x^2-30x=65\)

\(\Leftrightarrow-65x=65\)

\(\Leftrightarrow x=-1\)

Vậy...

b, \(4x\left(3x+5\right)+6x\left(7-2x\right)=-124\)

\(\Leftrightarrow12x^2+20x+42x-12x^2=-124\)

\(\Leftrightarrow62x=-124\)

\(\Leftrightarrow x=-2\)

Vậy...

c, \(\left(3x-2\right)\left(2x+3\right)-6x\left(x+5\right)=69\)

\(\Leftrightarrow6x^2+9x-4x-6-6x^2-30x=69\)

\(\Leftrightarrow-25x=75\)

\(\Leftrightarrow x=-3\)

Vậy...

Answer 2

a) 5x(4x - 7) - 10x(2x + 3) = 65

\(\Leftrightarrow\) 20x² - 35x - 20² - 30x = 65

\(\Leftrightarrow\) -65x = 65

\(\Leftrightarrow\) -65x = 65

\(\Leftrightarrow\) x = \(\dfrac{65}{-65}=-1\)

b) 4x(3x + 5) + 6x(7 - 2x) = -124

\(\Leftrightarrow\) 12x² + 20x + 42x - 12x² = -124

\(\Leftrightarrow\) 62x = -124

\(\Leftrightarrow\) x = \(\dfrac{-124}{62}=-2\) 

c) (3x - 2)(2x + 3) - 6x(x + 5) = 69

\(\Leftrightarrow\) 6x² + 5x - 6 - 6x² - 30x = 69

\(\Leftrightarrow\) -25x = 69 + 6

\(\Leftrightarrow\) -25x = 75

\(\Leftrightarrow\) x = \(\dfrac{75}{-25}\) = -3

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Answer 3

a) Ta có: \(5x\left(4x-7\right)-10x\left(2x+3\right)=65\)

\(\Leftrightarrow20x^2-35x-20x^2-30x=65\)

\(\Leftrightarrow-65x=65\)

hay x=-1

Vậy: x=-1

b) Ta có: \(4x\left(3x+5\right)+6x\left(7-2x\right)=-124\)

\(\Leftrightarrow12x^2+20x+42x-12x^2=-124\)

\(\Leftrightarrow62x=-124\)

hay x=-2

Vậy: x=-2