Question

Tìm x , biết :

a) x.(x+5)-(x+3)²=0

b) (2x+1)²-(4x-3).(x+1)=10

c) (x-5)²-(x+7)²=20-3x

Answer 1

a) x(x + 5) - (x + 3)² = 0

<=> x² + 5x - (x² + 2.x.3 + 3²) = 0

<=> x² + 5x - x² - 6x - 9 = 0

<=> -x - 9 = 0

<=> -x = 9

<=> x = -9

b) (2x + 1)² - (4x - 3)(x + 1) = 10

<=> 4x² + 4x + 1 - (4x² + 4x - 3x - 3) = 10

<=> 4x² + 4x + 1- 4x² - 4x + 3x + 3 = 10

<=> 3x + 4 = 10

<=> 3x = 6

<=> x = 2

c) (x - 5)² - (x + 7)² = 20 - 3x

<=> (x - 5 - x - 7)( x - 5 +x + 7) = 20 - 3x

<=> -12(2x + 2) = 20 - 3x

<=> -24x - 24 = 20 - 3x

<=> -24x + 3x = 20 + 24

<=> -21x = 44

<=> x = \(-\frac{44}{21}\)