Explain this simplification

[Thethinggoessqrt]

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

What happened here? Where did one ^2 or (a+b) go?

 

[tkhunny]

Please factor this: x^2 + xy