第22页 - 通城学典课时作业本七年级数学苏科版江苏专用

C

D

$x²+9x+18$

$x²−5x+4$

$2y²−\frac{1}{6}y−\frac{1}{6}$

$mn+2m−3n−6$

−4

$ \begin{aligned}解：原式&=2a^2-ab+6ab-3b^2 \\ &=2a^2+5ab−3b^2 \\ \end{aligned}$

$ \begin{aligned}解：原式&=8x^2-2x^4-12+3x^2 \\ &=-2x^4+11x^2-12 \\ \end{aligned}$

$ \begin{aligned}解：原式&=x^3+x^2+x-x^2-x-1 \\ &=x^3-1 \\ \end{aligned}$

$ \begin{aligned}解：原式&=a^2-3a+3a-9-a^2+2a \\ &=2a-9 \\ \end{aligned}$

$解：∵a^2-5=-3ab$

$∴a^2+3ab=5$

$(a+b)(a+2b)-2b^2=a^2+2ab+ab+2b^2-2b^2=a^2+3ab=5$

B

A