Ta có $ 5x^2 \ge 0 \to 5x^2 +5 > 0$
$\to |5x^2 +5| = 5x^2+5$
$\to M = 5x^2 +5 + |2x+1| + 2004 - 5x^2 = |2x+1| + 2009$
Ta có $ |2x+1|\ge 0 \to |2x+1| + 2009 \ge 2009$
$\to M_{min} = 2009$
Dấu $=$ xảy ra khi $ 2x +1 = 0 \to 2x = -1 \to x = \dfrac{-1}{2}$