(cos θ + sin θ)² + (cos θ - sin θ)² is equal to

1. -2

2. 0

3. 1

4. 2

Given, (cos θ + sin θ)² + (cos θ - sin θ)²

On solving,

⇒ cos² θ + sin² θ + 2cos θ sin θ + cos² θ + sin² θ - 2cos θ sin θ
⇒ 2(cos² θ + sin² θ)
⇒ 2.

Hence, Option 4 is the correct option.