Đáp án: + Giải thích các bước giải:
bài 2
$A = (3x + y)² - 3y(2x - \dfrac{1}{3}y)$
$= 9x² + 6xy + y² - 6xy + y²$
$= 9x² + 2y²$
$B = (x-5)(x+5) - (x-8)(x+4)$
$= x² - 25 - (x² - 4x - 24)$
$= x² - 25 - x² + 4x + 24$
$= $4x - 1$
$C = (x-2)² +(x+2)² - 2(x-2)(x-2)$
$= x² - 4x + 4 + x² + x² + 4x + 4 - 2(x² - 4x + 4)$
$= 2x² + 8 - 2x² + 8x - 8$
$= 8x$
bài 1)
a) $A = x ; B = 2$
$1) x² + 4x + 2² = (x+2)²$
$2) x² - 4x + 2² = (x-2)²$
$3) x² - 2² = (x-2)(x+2)$
$4) (x - 2)³ = x³ - 6x² + 12x - 8$
$5) (x+2)² = x³ + 6x² + 12x + 8$
$6) x³ - 2³ = (x-2)(x² + 2x + 4)$
$7) x³ + 2³ = (x+2)(x² - 2x + 4)$
b) A = x ; B = 3
$1) x² + 6x + 3² = (x+3)²$
$2) x² - 6x + 2² = (x-3)²$
$3) x² - 3² = (x-3)(x+3)$
$4) (x - 3)³ = x³ - 9x² + 27x - 9$
$5) (x+3)² = x³ + 9x² + 27x + 9$
$6) x³ - 3³ = (x-3)(x² + 3x + 9)$
$7) x³ + 3³ = (x+2)(x² - 3x + 9)$
