Proving Non-negativity of Quadratic Inequalities for All x

Prove that for all values of $x$, the following inequalities hold:
a) $x^2 + 2x + 1 \geq 0$
b) $9x^2 - 6x + 1 \geq 0$
c) $x^2 - 4x + 3 \geq -1$
d) $x^2 + x + 2 \geq 0$