a+c-7=0,(a+b)^2-2a(b-c)-2b(b-c)+(c-b)^2
a+c-7=0a+c=7(a+b)^2-2a(b-c)-2b(b-c)+(c-b)^2=a^2+b^2+2ab-2ab+2ac-2b^2+2bc+c^2+b^2-2bc=a^2+2ac+c^2=(a+c)^2=49
a+c-7=0,(a+b)^2-2a(b-c)-2b(b-c)+(c-b)^2
a+c-7=0a+c=7(a+b)^2-2a(b-c)-2b(b-c)+(c-b)^2=a^2+b^2+2ab-2ab+2ac-2b^2+2bc+c^2+b^2-2bc=a^2+2ac+c^2=(a+c)^2=49