c) x² - 6x + 9
= x² - 2 . x . 3 + 3²
= (x - 3)²
d) 4x² - 4x + 1
= (2x)² - 2 . 2x . 1 + 1
= (2x - 1)²
e) 9x² - 6x + 1
= (3x)² - 2 . 3x . 1 + 1
= (3x - 1)²
f) 25x² - 40x + 16
= (5x)² - 2 . 5x . 4 + 4²
= (5x - 4)²
g) x² - 1
= (x - 1) (x + 1)
h) (2x + 3)² - 25
= (2x + 3)² - 5²
= (2x + 3 - 5) (2x + 3 + 5)
= (2x - 2) (2x + 8)
= 2 (x - 1) 2 (x + 4)
= 4 (x - 1) (x + 4)
i) 25x² - 9y²
= (5x)² - (3y)²
= (5x - 3y) (5x + 3y)
j) (3x + 2)² - (x + 1)²
= (3x + 2 + x + 1) (3x + 2 - x - 1)
= (4x + 3) (2x + 1)
