1) Giải a) \( x^3 + x^2 - 4x - 4 = 0 \) b) \( \frac{1}{x+1} + \frac{2x+1}{x^3+1} = \frac{2}{x^2+x+1} \) c) \( x^2 - y^2 + 2x - 4y - 10 = 0 \) (với \( x, y \in \mathbb{N} \))