## Algebra 1: Common Core (15th Edition)

$a^{2}+b^{2}+c^{2}+2ab+2bc+2ac$
Addition is associative, we can write $a+b+c$ as a sum of two terms: $(a+b+c)^{2}=[(a+b)+c]^{2}$ ... and we now square the binomial $=(a+b)^{2}+2(a+b)(c)+c^{2}$ ... square the binomial, distribute $2c(a+b)$... $=a^{2}+2ab+b^{2}+2ac+2bc+c^{2}$ ... simplify =$a^{2}+b^{2}+c^{2}+2ab+2bc+2ac$