a. ...+...-...+4bc+ab-4c=6ab+2bc b.

a. ...+...-...+4bc+ab-4c=6ab+2bc b. (a+b+c)^2=[(...+...)+c]^2 =(...+...)^2+2...(a+b)+...^2 =...^2+...^2+2ab+2...+2...+...^2 = a^2+b^2+c^2+2(...+...+...)