Question

I'm pretty sure d) is supposed to be 3a^2 - 3b^2. Where have I gone wrong?

Answer 1

$(2a+b)^2-(a+2b)^2 \\ (4a^2+4ab+b^2)-(a^2+4ab+4b^2) \\ (4a^2+4ab+b2-a^2-4ab-4b^2) \\ (3a^2-3b^2) Final Answer$