woa

a. x(x + 7) - (x - 2)(x + 3) = 0

<=> x² + 7x - (x² + 3x - 2x - 6) = 0

<=> x² + 7x - x² - 3x + 2x + 6 = 0

<=> x² - x² + 7x - 3x + 2x + 6 = 0

<=> 6x + 6 = 0

<=> 6x = -6

<=> x = -1

b. (x + 2)² - x² + 4 = 0

<=> (x + 2 - x)(x + 2 + x) + 4 = 0

<=> 2(2 + 2x) + 4 = 0

<=> 4(1 + x) + 4 = 0

<=> 4(1 + x) = -4

<=> 1 + x = -1

<=> x = -1 - 1

<=> x = -2

b. x² - 3x + xy - 3y

= x(x - 3) + y(x - 3)

= (x + y)(x - 3)

c. x² - 5x + 4

= x² + x + 4x + 4

= x(x + 1) + 4(x + 1)

= (x + 4)(x + 1)

Có 2 TH: 

TH1: x = \(\dfrac{-4}{3}\)

TH2: x = \(\dfrac{4}{3}\)