5a(a+b+c)-5b(a-b-c)-5c(a+b-c) ПОЖАЛУЙСТА!=)

5a(a+b+c)-5b(a-b-c)-5c(a+b-c)=5a*a+5ab+5ac-5ab+5bb+5bc-5ac-5cb+5cc=5a*a+5bb+5cc=5(a*a+b*b+c*c)

5a(a+b+c)-5b(a-b-c)-5c(a+b-c) = 5a^2+5ab+5ac-5ab+5b^2+5bc-5ac-5bc+5c^2=5a^2+5b^2+5c^2