Em tham khảo:
a. $\frac{x^2+2}{x^3-1}$+ $\frac{x+1}{x^2+x+1}$+ $\frac{1}{1-x}$
⇔$\frac{x^2+2}{(x-1)(x^2+x+1)}$+ $\frac{(x+1)(x-1)}{(x-1)(x^2+x+1)}$-$\frac{x^2+x+1}{(x-1)(x^2+x+1)}$
⇔$\frac{x^2+2+x^2-1-x^2-x-1}{(x-1)(x^2+x+1)}$
⇔$\frac{x(x-1)}{(x-1)(x^2+x+1)}$
⇔$\frac{x}{x^2+x+1}$
b. M<$\frac{1}{3}$
⇔$\frac{x}{x^2+x+1}$<$\frac{1}{3}$
⇔$x^{2}$+x+1>3x
⇔$(x-1)^{2}$ >0
⇔x khác 1
Vậy........
