Question

a b c属于R,求证a的二次方+b的二次方+c的二次方大于等于2(a+b+c)-3

Answer 1

(a-1)^2+(b-1)^2+(c-1)^2 ≥ 0

a^2-2a+1+b^2-2b+1+c^2-2c+1 ≥ 0

a^2+b^2+c^2-2(a+b+c)+3 ≥ 0

a^2+b^2+c^2 ≥ 2(a+b+c)-3