Giải bài tập 6.22 trang 19 Toán 8 tập 2 KNTT

a)$\frac{1}{x}+\frac{2}{x+1}+\frac{3}{x+2}-\frac{1}{x}-\frac{2}{x+1}-\frac{3}{x+2}$

=$\frac{2}{x+1}-\frac{2}{x-1}=\frac{2(x-1)-2(x+1)}{(x+1)(x-1)}$

=$\frac{2x-2-2x-2}{(x+1)(x-1)}=\frac{-4}{(x+1)(x-1)}$

b)$\frac{2x-1}{x}+\frac{1-x}{2x+1}+\frac{3}{x^{2}-9}+\frac{1-2x}{x}+\frac{x-1}{2x+1}-\frac{3}{x+3}$

=$\frac{2x-1}{x}+\frac{1-2x}{x}+\frac{1-x}{2x+1}+\frac{x-1}{2x+1}+\frac{3}{x^{2}-9}-\frac{3}{x+3}$

=$\frac{3}{x^{2}-9}-\frac{3}{x+3}$

=$\frac{3}{(x-3)(x+3)}-\frac{3}{x+3}$

=$\frac{3-3(x-3)}{(x-3)(x+3)}$

=$\frac{12-3x}{(x-3)(x+3)}$