18) -$$\frac{5}{6}$$a +$$\frac{7}{8}$$b +$$\frac{7}{12}$$a -$$\frac{5}{12}$$b =

18) -$$\frac{5}{6}$$a +$$\frac{7}{8}$$b +$$\frac{7}{12}$$a -$$\frac{5}{12}$$b = -$$\frac{5}{6}$$a +$$\frac{7}{12}$$a +$$\frac{7}{8}$$b -$$\frac{5}{12}$$b = -$$\frac{5\cdot2}{6\cdot2}$$a +$$\frac{7}{12}$$a +$$\frac{7\cdot3}{8\cdot3}$$b -$$\frac{5\cdot2}{12\cdot2}$$b = -$$\frac{10}{12}$$a +$$\frac{7}{12}$$a +$$\frac{21}{24}$$b -$$\frac{10}{24}$$b = -$$\frac{3}{12}$$a + $$\frac{11}{24}$$b = -$$\frac{1}{4}$$a + $$\frac{11}{24}$$b

Ответ: -$$\frac{1}{4}$$a + $$\frac{11}{24}$$b