$M=\frac{x^{4}+2}{x^{6}+1}+\frac{x^{2}-1}{x^{4}-x^{2}+1}+\frac{x^{2}+3}{x^{4}+4x^{2}+3}$
$M= \frac{x^{4}+2}{x^{6}+1}+\frac{(x^{2}-1)(x^{2}+1)}{(x^2+1)(x^{4}-x^{2}+1)}+\frac{x^{2}+3}{(x^{2}+1)(x^{2}+3)}$
$M= \frac{x^{4}+2}{x^{6}+1}+\frac{(x^{4}-1)}{x^{6}+1}+\frac{1}{(x^{2}+1)}$
$M=\frac{x^{4}+2+x^{4}-1}{x^{6}+1}+\frac{x^{4}-x^{2}+1}{(x^{2}+1)(x^{4}-x^{2}+1)}$
$M = \frac{2x^{4}+1}{x^{6}+1}+\frac{x^{4}-x^{2}+1}{x^{6}+1}$
$M=\frac{3x^{4}-x^{2}+2}{x^{6}+1}$