Question

Tìm x biết:

a, 5x.(x-3) - 4x.( x+1)= (x-2).(x+2)

b, 3x.( x-5 )+( 2x+1).( x-3) = 5x.(x-1)

các pạn giúp với nhe! mk cảm ơn!

Answer 1

a)\(5x\left(x-3\right)-4x\left(x+1\right)=\left(x-2\right)\left(x+2\right)\)

\(\Leftrightarrow5x^2-15x-4x^2-4x=x^2-4\)

\(\Leftrightarrow x^2-19x-x^2+4=0\)

\(\Leftrightarrow4-19x=0\Leftrightarrow19x=4\Leftrightarrow x=\dfrac{4}{19}\)

b)\(3x\left(x-5\right)+\left(2x+1\right)\left(x-3\right)=5x\left(x-1\right)\)

\(\Leftrightarrow3x^2-15x+2x^2-5x-3=5x^2-5x\)

\(\Leftrightarrow5x^2-20x-3-5x^2+5x=0\)

\(\Leftrightarrow-15x-3=0\)\(\Leftrightarrow-15x=3\Leftrightarrow x=-\dfrac{1}{5}\)

Answer 2

a, \(5x\left(x-3\right)-4x\left(x+1\right)=\left(x-2\right)\left(x+2\right)\)

\(\Leftrightarrow5x^2-15x-4x^2-4x=x^2-4\)

\(\Leftrightarrow x^2-19x=x^2-4\)

\(\Leftrightarrow19x=4\)

\(\Leftrightarrow x=\dfrac{4}{19}\)

Vậy...

b, \(3x\left(x-5\right)+\left(2x+1\right)\left(x-3\right)=5x\left(x-1\right)\)

\(\Leftrightarrow3x^2-15x+2x^2-6x+x-3=5x^2-5x\)

\(\Leftrightarrow5x^2-20x-3=5x^2-5x\)

\(\Leftrightarrow-20x-3=-5x\)

\(\Leftrightarrow-15x=3\)

\(\Leftrightarrow x=\dfrac{-1}{5}\)

Vậy...

Answer 3

a) 5x.(x-3) - 4x.(x+1) = (x-2).(x+2)

5x² - 15x - 4x² - 4x = x² - 4

5x² -15x -4x² - 4x - x² - 4 = 0

-19x + 4 = 0

-19x = -4

x = \(\dfrac{4}{19}\)

b) 3x( x-5) + (2x+1)(x-3) = 5x(x-1)

3x² - 15x + 2x² - 6x + x -3 = 5x² - 5x

3x² - 15x + 2x² - 6x + x -3 - 5x² + 5x = 0

-15x - 3 =0

x = \(-\dfrac{1}{5}\)

Answer 4

a,

\(5x\left(x-3\right)-4x\left(x+1\right)=\left(x-2\right)\left(x+2\right)\)

=> \(5x^2-15x-4x^2-4x=x^2-4\)

=> \(x^2-19x=x^2-4\)

=> \(19x=4\)

=> \(x=\dfrac{4}{19}\)

Vậy \(x=\dfrac{4}{19}\)

b,\(3x\left(x-5\right)+\left(2x+1\right)\left(x+3\right)=5x\left(x-1\right)\)

=> \(3x^2-15x+2x^2+6x+x+3=5x^2-5x\)

=> \(5x^2-8x+3=5x^2-5x\)

=> -8x + 3 = -5x

=> -3x = -3

=> x = 1

Vậy x = 1