Đáp án: + Giải thích các bước giải:
$1$. $(x+5)(x-7)-(x-4)(x+3)$
$= (x^2 + 5x - 7x - 35) - (x^2 - 4x + 3x - 12)$
$= x^2 - 2x - 35 - x^2 + x + 12$
$= -x-23$.
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$2$. $(x-1)(x+2)-(x+5)(x-2)$
$= (x^2 - x+2x -2) - (x^2 + 5x -2x - 10)$
$= x^2 + x - 2 - x^2 - 3x + 10$
$= -2x+8$.
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$3$. $(2x-3)(x+4)+(-x+1)(x-2)$
$= (2x^2 - 3x + 8x - 12) + (1-x)(x-2)$
$= 2x^2 + 5x - 12 - x^2 + x + 2x - 2$
$= x^2 + 8x - 14$.
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$4$. $(-x+5)(x-3)+(2x-1)(x+3)$
$= (5-x)(x-3) + (2x-1)(x+3)$
$= 5x - 15 - x^2 + 3x + 2x^2 - x + 6x - 3$
$= x^2 + 13x - 18$.
