Gap between neighbouring squares

Factor the expression as a product of a sum and a difference.

1. Use $a^2-b^2=(a-b)(a+b)$ with $a=51$ and $b=49$.
2. Then $a-b=2$ and $a+b=100$.
3. The product is $2\times 100$.
4. So the value is $200$.

Answer: $200$