第53页 - 江苏版实验班提优训练数学七年级上下册答案

C

D

$20x$

$y⁴-18y²+81$

-3x²+4xy+3y²

$x²+7x+1$

13

解：原式=[(a+b)+(a-b)][(a+b)-(a-b)]+a(1-4b)

=2a·2b+a-4ab

=a.

$ \begin{aligned}解：原式&=\frac{1}{4}a²-ab+b²-\frac{1}{4}a²+\frac{1}{4}b² \\ &=-ab+\frac{5}{4}b². \\ \end{aligned}$

$解：原式=(a²-1)²=a⁴-2a²+1.$

A

63

5

$解：原式=9-25a²+9+30a+25a²=30a+18.$

$ \begin{aligned}解：原式&=9b²-4a²-(a²-6ab+9b²) \\ &=9b²-4a²-a²+6ab-9b² \\ &=-5a²+6ab. \\ \end{aligned}$

$ ∵|a-1|+(b+2)²=0,$

$∴a-1=0,b+2=0,$

$ ∴a=1,b=-2,$

$ \begin{aligned}∴原式&=-5×1²+6×1×(-2) \\ &=-5×1-12 \\ &=-5-12 \\ &=-17. \\ \end{aligned}$