2020-2021学年最新华东师大版八年级数学上学期期(13)

(2)(-3a 2bc)3·3a 2b 2(13

bc)2-(-3ab 2c)2·(-a 2bc)3. 解:(1)(-32xy 2)2·(-13

x 2yz)3÷xyz 2 =9x 2y 4·(-1x 6y 3z 3)÷xyz 2 =-112x 7y 6z.

(2)(-3a 2bc)3·3a 2b 2(13

bc)2-(-3ab 2c)2· (-a 2bc)3

=-27a 6b 3c 3·3a 2b 2·19

b 2

c 2+9a 2b 4c 2·a 6b 3c 3 =-9a 8b 7c 5+9a 8b 7c 5

=0.

20.(8分)先化简,后求值:(2x-y)2-(y-2x)(-y-2x)+y(3x-2y), 其中x,y 满足|x+3y+7|+√C 3-8=0. 解:因为|x+3y+7|+√C 3-8=0, 所以x+3y+7=0,x 3-8=0, 解得x=2,y=-3.

(2x-y)2-(y-2x)(-y-2x)+y(3x-2y) =4x 2-4xy+y 2+y 2-4x 2+3xy-2y 2 =-xy,