代数式的运算问题(问题在书里)。

=-x+2x？+5+3-4x？+6倍

=-2x？+5x+8

②(3ab-7)(-4a？+6ab+7)

=3ab×(-4a？)+3ab×6ab+3ab×7-7×(-4a？)-7×6ab-7×7

=-12a？b+18a？b？+21ab+28a？-42ab-49

=-12a？b+18a？b？+28a？-21ab-49

①36a？bc-48ab？c+24abc？

=12abc(3a-4b+2c)

②2x？-3x-5

=(2x-5)(x+1)