Answer:
See explanation below.
Step-by-step explanation:
We know that all squares are positive. Even the square of a negative number is positive ((-2)²= 4).
Therefore, we can say that (a-b)²≥0
⇒a²-2ab+b² ≥ 0
⇒a² + b² ≥ 2ab
Please notice that I added the possibility that (a-b)² "equals zero" and not only "it's greater than zero" because we don't know if a ≠ b. Since the problem doesn't state anything about this fact, there's the possibility that a = b, and then we would have that a - b = 0 and therefore (a - b)² = 0.
