27x³ - 48x in the form of factors is :

1. 3(3x - 4)(3x - 4)

2. 3x(3x + 4)(3x + 4)

3. 3(3x² - 4x)(3x + 4)

4. 3x(3x - 4)(3x + 4)

x² - (x - 4y)² in the form of factors is :

1. 8y(x - 2y)

2. 8y(x + 2y)

3. 4y(x + 2y)

4. 4y(x - 2y)

Factorise :

a² - (2a + 3b)²

Factorise :

25(2a - b)² - 81b²