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第20页

信息发布者：

$4a - 2b + 6c$

$-5a + 2x - 3$

$3x + 4y - 7z - 3$

$-3a^3 - 2x^2 + 5x + 1$

$x^2 - 2xy + y^2$

$c - b$

$-3x^2 + 4y^2$

$3p + 1$

 解：原式=$a - (2a - 2) = a - 2a + 2 = -a + 2$

解：原式= $-(5x + y) - 3(2x - 3y) = -5x - y - 6x + 9y = -11x + 8y$

解：原式= $2x^2 - (7 + x) - (3x + 4x^2) = 2x^2 - 7 - x - 3x - 4x^2 = -2x^2 - 4x - 7$

解：原式= $-(3a^2 - 2a + 1) + (a^2 - 5a + 7) = -3a^2 + 2a - 1 + a^2 - 5a + 7 = -2a^2 - 3a + 6$

解：原式= $a^2 - 3[a^2 - 2(a^2 - a) + 1] = a^2 - 3[a^2 - 2a^2 + 2a + 1] = a^2 - 3[-a^2 + 2a + 1] = a^2 + 3a^2 - 6a - 3 = 4a^2 - 6a - 3$

解：原式= $3a^2b - 2[ab^2 - 2(a^2b - 2ab^2)] = 3a^2b - 2[ab^2 - 2a^2b + 4ab^2] = 3a^2b - 2[5ab^2 - 2a^2b] = 3a^2b - 10ab^2 + 4a^2b = 7a^2b - 10ab^2$

解：原式= $5a^2 - [3a - (2a - 3) + 4a^2] = 5a^2 - [3a - 2a + 3 + 4a^2] = 5a^2 - [a + 3 + 4a^2] = 5a^2 - a - 3 - 4a^2 = a^2 - a - 3$

解：原式= $2(a^2b - 3ab^2) - 3(2ab^2 - \frac{5}{6}a^2b) = 2a^2b - 6ab^2 - 6ab^2 + \frac{5}{2}a^2b = \frac{9}{2}a^2b - 12ab^2$