5.86 Упростите выражение: a) 0,4n - 0,7m – 0,9n + 0,7m; б) 6с - 8с - 4c + 21 - 13; в) \frac{3}{4}a + \frac{5}{6}b - \frac{1}{8}a - \frac{1}{3}b; г) \frac{7}{9}x - \frac{3}{4} - \frac{11}{18}x - \frac{1}{4}; д) 0,3m - \frac{2}{7} - 3m + \frac{6}{7}; e) \frac{1}{7}a + \frac{1}{4}c - \frac{1}{7}a + \frac{3}{4}c.

a) 0,4n - 0,7m – 0,9n + 0,7m = (0,4n - 0,9n) + (-0,7m + 0,7m) = -0,5n + 0 = -0,5n

б) 6с - 8с - 4c + 21 - 13 = (6c - 8c - 4c) + (21 - 13) = -6c + 8 = 8 - 6c

в) \(\frac{3}{4}a + \frac{5}{6}b - \frac{1}{8}a - \frac{1}{3}b = (\frac{3}{4}a - \frac{1}{8}a) + (\frac{5}{6}b - \frac{1}{3}b) = (\frac{6}{8}a - \frac{1}{8}a) + (\frac{5}{6}b - \frac{2}{6}b) = \frac{5}{8}a + \frac{3}{6}b = \frac{5}{8}a + \frac{1}{2}b\)

г) \(\frac{7}{9}x - \frac{3}{4} - \frac{11}{18}x - \frac{1}{4} = (\frac{7}{9}x - \frac{11}{18}x) + (-\frac{3}{4} - \frac{1}{4}) = (\frac{14}{18}x - \frac{11}{18}x) + (-\frac{4}{4}) = \frac{3}{18}x - 1 = \frac{1}{6}x - 1\)

д) 0,3m - \(\frac{2}{7}\) - 3m + \(\frac{6}{7}\) = (0,3m - 3m) + (-\(\frac{2}{7}\) + \(\frac{6}{7}\)) = -2,7m + \(\frac{4}{7}\)

e) \(\frac{1}{7}a + \frac{1}{4}c - \frac{1}{7}a + \frac{3}{4}c = (\frac{1}{7}a - \frac{1}{7}a) + (\frac{1}{4}c + \frac{3}{4}c) = 0 + \frac{4}{4}c = c\)