1) Cho a, b, c > 0, a + b + c = 3 thì m \[ a^2 + b^2 + c^2 \geq 3 \] 2) \[ \frac{3}{a^2 + b^2 + c^2} + a^2 + b^2 + c^2 \geq 4 \] 3) \[ ab + bc + ca \geq \frac{3}{4} \]