4. Привести подобные слагаемые.

1) $$-a + b + 2a - 3b = (-1+2)a + (1-3)b = a - 2b$$ 2) $$4x - 3y - x + y = (4-1)x + (-3+1)y = 3x - 2y$$ 3) $$3m - 4n + 2n - 3m = (3-3)m + (-4+2)n = 0m - 2n = -2n$$ 4) $$7a - 10b + b - 7a = (7-7)a + (-10+1)b = 0a - 9b = -9b$$ 5) $$25k - 12n + 7k + 7n + 12n = (25+7)k + (-12+7+12)n = 32k + 7n$$ 6) $$0,5m + 2z + 5m - 4z - 5m = (0,5+5-5)m + (2-4)z = 0,5m - 2z$$ 7) $$7n - 7m + 0,1m - 0,1n = (-7+0,1)m + (7-0,1)n = -6,9m + 6,9n$$ 8) $$0,09a + 0,01b - 0,9a + 0,9b = (0,09-0,9)a + (0,01+0,9)b = -0,81a + 0,91b$$ 9) $$0,5z + \frac{1}{2}k - 5z - 0,5k = (0,5 - 5)z + (\frac{1}{2} - 0,5)k = -4,5z + 0k = -4,5z$$ 10) $$\frac{1}{2}a + 0,25b - a - \frac{1}{4}b = (\frac{1}{2} - 1)a + (0,25 - \frac{1}{4})b = -\frac{1}{2}a + 0b = -\frac{1}{2}a$$ 11) $$-2a + 3c + 5a - 7c - a + c = (-2+5-1)a + (3-7+1)c = 2a - 3c$$ 12) $$4k - 2n - 7k - n + k + 4n = (4-7+1)k + (-2-1+4)n = -2k + n$$ 13) $$-\frac{3}{8}a - 2\frac{3}{4}b + \frac{5}{8}a - \frac{1}{4}b = (-\frac{3}{8} + \frac{5}{8})a + (-2\frac{3}{4} - \frac{1}{4})b = \frac{2}{8}a - 3b = \frac{1}{4}a - 3b$$ 14) $$\frac{5}{9}a - 3\frac{1}{7}b - \frac{8}{9}a - \frac{6}{7}b = (\frac{5}{9} - \frac{8}{9})a + (-3\frac{1}{7} - \frac{6}{7})b = -\frac{3}{9}a + (-3\frac{7}{7})b = -\frac{1}{3}a - 4b$$