The second one because if you foil (first, inside, outside, last) out each of the equations than that’s the only on that is equal.
The math to support it is first you rewrite the equation as (a + 2b)(a + 2b),
then you multiply the two numbers in the first spot, a and a which gives you a^2. Next you multiply the inside numbers 2b and a, which gives you 2ab.
Then you multiply the outside numbers 2b and a, which gives you 2ab.
Finally, you multiply the last numbers, 2b and 2b which gives you 4b^2.
So the equation you now have is:
a^2 + 2ab + 2ab + 4b^2 and simplified is
a^2 + 4ab + 4b^2
