EXTRA 2AB

Mathematics mein a square+b square kare to result kya aata hai, lekin maan lijiye a+b × square(^2) × () square(^2) kare toh? a+b × () square(^2) kare toh? Toh result aata hai a square (^2) + 2ab+ b square(^2), ek extra 2ab milta hai ki nahi milta hai? Ye extra 2ab kaha se aaya?