c) x² + 6x + 9 = (x + 3)²
d) x² - 4x + 4 = (x - 2)²
e) x² - 25 = (x - 5)(x + 5)
f) 4x² + 4x + 1 = (2x + 1)²
g) 9x² + 12x + 4 = (3x + 2)²
h) 9x² - 25 = (3x - 5)(3x + 5)
i) x² + 10x + 16 =
= x² + 8x + 2x + 16
= x(x + 8) + 2(x + 8)
= (x + 2)(x + 8)
j) x² + 5x + 6 =
= x² + 3x + 2x + 6
= x(x + 3) + 2(x + 3)
= (x + 2)(x + 3)
k) x² - 2x - 15 =
= x² + 3x - 5x - 15
= x(x + 3) - 5(x + 3)
= (x - 5)(x + 3)