5.86 Упростите выражение: a) 0,4n – 0,7m – 0,9n + 0,7m; б) 6с – 8с – 4c + 21 – 13; в) 3/4 a + 5/6 b – 1/8 a – 1/3 b;

a) \(0.4n - 0.7m - 0.9n + 0.7m = (0.4n - 0.9n) + (-0.7m + 0.7m) = -0.5n + 0 = -0.5n\)

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

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

Ответ:

• a) \(-0.5n\)
• б) \(-6c + 8\)
• в) \(\frac{5}{8}a + \frac{1}{2}b\)