Question

3(a+b)^2-(2a+b)(2a-b)

Answer 1

3(a^2+2ab+b^2)-(4a^2-b^2)
3a^2+6ab+3b^2-4a^2+b^2
-a^2+6ab+4b^2

Answer 2

$3(a+b)^2-(2a+b)(2a-b)=3(a^2+2ab+b^2)-(4a^2-b^2)= \ =3a^2+6ab+3b^2-4a^2+b^2=-a^2+6ab+4b^2$