2)
a, x² - 10x + 25
= x² - 10x + 5²
= (x - 5)² HĐT số 2
b, 9 - 6y + y²
= 3² - 6y + y²
= (3 - y)²
c, x² - 4y²
= x² - (2y)²
= (x - 2y).(x + 2y)
d, x² + 4xy + 2y² + 4y + 4
Mk giải mãi không ra
3,
a, (x + 1)² - (x - 1)² - 3(x + 1)(x - 1)
= −3x² + 4x + 3
b, 5(x + 2)(x - 2) - $\frac{1}{6}$(6 - 8x)² + 17
= 5x +10 ( x-2 ) - $\frac{1}{6}$.6 -$\frac{1}{6}$ . 8x + 17
= 5x + 10x - 20 - 1 - $\frac{4}{3}$x + 17
= $\frac{41}{3}$x - 4
= $\frac{29}{3}$x