(x + y - z)(x - y + z) is equal to :

1. x² - y² - z² - 2yz

2. x² - y² - z² + 2yz

3. x² - y² + z² - 2yz

4. x² - y² + z² + 2yz

If (3x - 4y)² = 9x² + axy + 16y²; the value of a is :

1. -24

2. 24

3. -12

4. 12

In the expansion of (2x² - 8)(x - 4)²; find the value of :

(i) coefficient of x³

(ii) coefficient of x²

(iii) constant term.