4. Раскройте скобки и приведите подобные слагаемые: 1) 9(7x-6)-18x; 2) 7a-6(19-a); 3) 0,8(6x-2) + 1,6(x - 4); 4) 2,8(5b-6c)-(7b-8a) 1,2; 5)-(-4,9-5,8z) – (3,1z - 5,6); 6) 8/15(2 1/4a-7 1/2b)-7/30(4 2/7a-8 4/7b).

1) \(9(7x - 6) - 18x = 9 \cdot 7x - 9 \cdot 6 - 18x = 63x - 54 - 18x = 63x - 18x - 54 = 45x - 54\)

2) \(7a - 6(19 - a) = 7a - 6 \cdot 19 + 6 \cdot a = 7a - 114 + 6a = 7a + 6a - 114 = 13a - 114\)

3) \(0,8(6x - 2) + 1,6(x - 4) = 0,8 \cdot 6x - 0,8 \cdot 2 + 1,6 \cdot x - 1,6 \cdot 4 = 4,8x - 1,6 + 1,6x - 6,4 = 4,8x + 1,6x - 1,6 - 6,4 = 6,4x - 8\)

4) \(2,8(5b - 6c) - (7b - 8a) \cdot 1,2 = 2,8 \cdot 5b - 2,8 \cdot 6c - 1,2 \cdot 7b + 1,2 \cdot 8a = 14b - 16,8c - 8,4b + 9,6a = 14b - 8,4b - 16,8c + 9,6a = 5,6b - 16,8c + 9,6a = 9,6a + 5,6b - 16,8c\)

5) \(-(-4,9 - 5,8z) - (3,1z - 5,6) = 4,9 + 5,8z - 3,1z + 5,6 = 5,8z - 3,1z + 4,9 + 5,6 = 2,7z + 10,5\)

6) Должно быть \(\frac{8}{15}(2 \frac{1}{4}a - 7 \frac{1}{2}b) - \frac{7}{30}(4 \frac{2}{7}a - 8 \frac{4}{7}b)\). \(\frac{8}{15}(2 \frac{1}{4}a - 7 \frac{1}{2}b) - \frac{7}{30}(4 \frac{2}{7}a - 8 \frac{4}{7}b) = \frac{8}{15}(\frac{9}{4}a - \frac{15}{2}b) - \frac{7}{30}(\frac{30}{7}a - \frac{60}{7}b) = \frac{8}{15} \cdot \frac{9}{4}a - \frac{8}{15} \cdot \frac{15}{2}b - \frac{7}{30} \cdot \frac{30}{7}a + \frac{7}{30} \cdot \frac{60}{7}b = \frac{2 \cdot 3}{5}a - \frac{4}{1}b - a + \frac{2}{1}b = \frac{6}{5}a - 4b - a + 2b = (\frac{6}{5} - 1)a + (-4 + 2)b = \frac{1}{5}a - 2b\)