Answer:
-a^2 + 2 ab + b^2
Step-by-step explanation:
To solve this, you need to distribute the letters into the parenthesis.
Then, you sum equal things, and you get the result.
[tex]b(a+b)-a(a-b)=\\ba + b^{2} -a^{2} + ab=\\ b^{2} + 2ab -a^{2}[/tex]
So, the rigth answer is number three: -a^2 + 2 ab + b^2
