Cho a^2 + b^2 + c^2 = ab + bc + ca, Cho a^2 + b^2 + c^2 = |ab + bc + ca|, Cho a^2 + b^2 + c^2 = ab = bc = ca, Cho a^2+b^2+c^2=ab+bc+ca, Cho: a^2 + b^2 + c^2 = ab + bc + ca