a/ 9x ² - $\frac{1}{4}$
= (3x)² - ($\frac{1}{2}$)²
= (3x - $\frac{1}{2}$)(3x + $\frac{1}{2}$)
b/ (a - b) ² - 1
= (a - b - 1)(a - b + 1)
c/ (3x - 2y) ² - (2x - 3y) ²
= (3x - 2y - 2x + 3y)(3x - 2y + 2x - 3y)
= (x + y)(5x - 5y)
= 5(x + y)(x - y)
d/ ( a ² + 4) ² - 16a ²
= (a² + 4)² - (4a)²
= (a² - 4a + 4)(a² + 4a + 4)
= (a - 2)².(a + 2)²
e/4x ² - 12xy + 9y ²
= (2x)² - 2.2x.3y + (3y)²
= (2x - 3y)²
f/ (x+y) ² - 2(x + y) + 1
= (x + y)² - 2(x + y).1 + 1²
= (x + y - 1)²
g/ $x^{6}$ - y ³
= $x^{2.3}$ - y³
= (x²)³ - y³
= (x² - y)($x^{4}$ + x²y + y²)
h/ x ³ - 3x ² + 3x - 1
= (x - 1)³