Bài 1:
a) x² - 4x + 4
= (x)² - 2.2.x + (2)²
= (x - 2)²
b) x² - 8x + 16
= (x)² - 2.x.4 + (4)²
= (x - 4)²
c) x² - 4xy + 4y²
= (x)² - 2.x.2y + (2y)²
= (x - 2y)²
d) 10xy - 25y²
= 5y.(2x - 5y)
e) 10x - 25 - x²
= - (x² - 10x + 25)
= - [(x)² - 2.x.5 + (5)²]
= -(x - 5)²
Bài 2:
a) x² - 9y²
= (x)² - (3y)²
= (x - 3y)(x + 3y)
b) $\frac{4}{25}$x² - 36y²
= ($\frac{2}{5}$x)² - (6y)²
= ($\frac{2}{5}$x - 6y)($\frac{2}{5}$x + 6y)
c) $\frac{1}{25}$x² - 64y²
= ($\frac{1}{5}$x)² - (8y)²
= ($\frac{1}{5}$x - 8y)($\frac{1}{5}$x + 8y)
d) (x + 5)² - 16
= (x + 5)² - (4)²
= (x + 5 - 4)(x + 5 + 4)
= (x + 1)(x + 9)
