1、4-12(x-y)+9(x-y)^2=()^2简便计算:2、1.2345^2+1.7655^2+2.469*0.7655先化简,后求值.3、已知x^2-x=5,求2x(x-1)-(2x-1)^2的值.4、已知|x+2y+1|+(2x-y-2)^2=0,求(2x-y)^2-2(2x-y)+(2x+y)^2的值.

问题描述:

1、4-12(x-y)+9(x-y)^2=()^2
简便计算:
2、1.2345^2+1.7655^2+2.469*0.7655
先化简,后求值.
3、已知x^2-x=5,求2x(x-1)-(2x-1)^2的值.
4、已知|x+2y+1|+(2x-y-2)^2=0,求(2x-y)^2-2(2x-y)+(2x+y)^2的值.

1、假设x-y=T,则原式为2²-12T+(3T)²,即(3T-2)²,所以答案是[3(x-y)-2]²
2、原式=1.2345²+2*1.2345*0.7655+1.7655²
=(1.2345+1.7655)²
=9
3、原式=2(x²-x)-(4x²-4x+1)
=2(x²-x)-(4(x²-x)+1)
=2*5-(4*5+1)
=10-21
=-11

1、2^2-2*2*3(x-y)+[3(x+y)]^2=(2-3x-3y)^2
2、第二题第三项是2.469*1.7655的话,原式=(1.2345+1.7655)^2=3^2=9
3、原式=-2(x^2-x)-1=-11
4、由题意得x+2y=-1 2x-y=2 所以x=3/5 y=-4/5 原式=2^2-2*2+(2/5)^2=4/25

(1)4-12(x-y)+9(x-y)^2=(3(x-y)-2)^2
(2)1.2345^2+1.7655^2+2.469*0.7655=1.2345^2+(1+0.7655)^2+2*1.2345*0.7655
=1+2*0.7655+0.7655^2+1.2345^2+2*1.2345*0.7655=4+1.531=5.531
(3)x^2-x=x(x-1)=5, 2x(x-1)-(2x-1)^2=10-4x^2+4x-1=9-4x(x-1)=-11
(4)因为|x+2y+1|+(2x-y-2)^2=0
所以x+2y+1=0, 2x-y-2=0
2x-y=2,x+2y=-1,x=3/5 y=-4/5
(2x-y)^2-2(2x-y)+(2x+y)^2=4-4+4/25=4/25

1.原式=2²-2*2*3(x-y)+(x-y)²=(2-x+y)²
第二题 若为
1.2345^2+1.7655^2+2.469*1.7655=1.2345^2+1.7655^2+2*1.2345*1.7655
=(1.2345+1.7655)²