If x + y - z = 4 and x² + y² + z² = 30, then find the value of xy - yz - zx.

The longest road that can be placed in a rectangular box = 20 cm and the sum of its length breadth and height is 30 cm. Find the total surface area of the box.

In (3x + 2)(x - 4), the coefficient of x is :

1. -14

2. 8

3. -10

4. 3

(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