第21页 - 通城学典课时作业本七年级数学苏科版江苏专用

D

C

$4xy$

8

2

$6m^2−\frac{3}{2}m$

$ \begin{aligned}解:2x²-2x-3x²-2x&=-x²-2x-12 \\ 2x²+x²-3x²-2x-2x+2x&=-12 \\ -2x&=-12 \\ x&=6 \\ \end{aligned}$

$ \begin{aligned}解:原式&=-4a³b³+6a²b²-8ab \\ &=-4(\mathrm {ab})³+6(\mathrm {ab})²-8ab \\ &=-4×3³+6×3²-8×3 \\ &=-78 \\ \end{aligned}$

$解：∵x^2-2x-1=0$

$∴x^2=2x+1$

$ ∴3x^3-10x^2+5x+2027=3x · x^2-10x^2+5x+2027$

$=3x(2x+1)-10x^2+5x+2027 $

$=6x^2+3x-10x^2+5x+2027 $

$ =-4x^2+8x+2027 $

$ =-4(2x+1)+8x+2027 $

$ =-8x-4+8x+2027 $

$=2023 $