第70页 - 经纶学典学霸七年级数学上下册【江苏国标】

D

C

(2-x)²(或(x-2)²)

(a+b)²

-(x-2y)²

(x-2)²

$2x或-2x或\frac{1}{4}x⁴$

$ \begin{aligned}解：原式&=4a²+20ab+25b² \\ &=(2a+5b)² \\ \end{aligned}$

$ \begin{aligned}解：原式&=x²y²-2xy+1 \\ &=(xy-1)² \\ \end{aligned}$

$ \begin{aligned} 解：原式&=-\frac{1}{2}(a²-4a+4) \\ &=-\frac{1}{2}(a-2)² \\ \end{aligned}$

$ \begin{aligned} 解：原式&=(a+b)²-4(a+b)+4 \\ &=[(a+b)-2]² \\ &=(a+b-2)² \\ \end{aligned}$

$ \begin{aligned}解：原式&=4+12(x-y)+9(x-y)² \\ &=[3(x-y)+2]² \\ &=(3x-3y+2)² \\ \end{aligned}$

B

6或-18

10000

58

-2

2

$ \begin{aligned}解：原式&=[(x²+1)-2x]² \\ &=(x-1)⁴. \\ \end{aligned}$

$ \begin{aligned}解：原式&=-[a²+6a(b-c)+9(b-c)²] \\ &=-(a+3b-3c)² \\ \end{aligned}$