Question

初一化简求值练习题及答案

Answer 1

（3X+2Y)+(4X+3Y)其中X=5,Y+3

原式=3X+2Y+4X+3Y=7X+5Y

当X=5,Y=3时

原式=5*7+（-3）*5+20

2.(5a^2-3b^2)+(a^2+b^2)-(5a^2+3b^2),其中a=-1,b=1
=5a^2-3b^2+a^2+b^2-5a^2-3b^2
=a^2-5b^2
=(-1)^2-5*1^2
=1-5
=-4

3.2(a^2b+ab^2)-2(a^2 b-1)-2ab^2 -2其中a=-2,b=2
=2a^2b+2ab^2-2a^2b+2-2ab^2-2
=0

1、已知A,B是方程x^2+2x-5=0的两个实数根,
求(A^2+2AB+2A)(B^2+2AB+2B)的值.
由A,B是方程x^2+2x-5=0的两个实数根得：
AB=-5，A+B=-2
A^2+2AB+2A)(B^2+2AB+2B)
=AB（A+2B+2）（B+2A+2）
=-5（-2+B+2）（-2+A+2）
=-5AB
=25

2、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y),其中x-y=6,xy=21.要详细步骤
化简得：
1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y)=
1/2[(x+y)方+2z(x+y)+z方]+1/2[(x-y)方-z方]-z(x+y)=
1/2(x+y)方+1/2(x-y)方=x方＋y方
由x-y=6,xy=21得，x方＋y方＝（x-y）方＋2xy＝78

3、a^2-ab+2b^2=3 求2ab-2a^2-4b^2-7的值
2ab-2a^2-4b^2-7
=2(ab-a^2-2b^2)-7
=-2(a^2-ab+2b^2)-7
=(-2)*3-7
=-6-7=-13

4、若A=2x^2+3xy-2x-3,B=-x^2+xy+2,且3A+6B的值与x无关，求y的值

3A+6B=6x^2+9xy-6x-9-6x^2+6xy+12
=15xy-6x+3
=x(15y-6)+3

5、9x+6x^2 -3(x-2/3x^2).其中x=-2
9x+6x?? -3(x-2/3x??)
=9x+6x??-3x+2x??
=8x??+6x
=8×(-2)??+6×(-2)
=32-12
=20

6、1/4(-4x^2+2x-8)-(1/2x-1),其中x=1/2
1/4(-4x??+2x-8)-(1/2x-1)
=-x??+1/2x-2-1/2x+1
=-x??-1
=-(1/2)??-1
=-1/4-1
=-5/4

7、3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz,其中x=-2,y=-3,z=1,
:3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz
=3x'y-2x'y+2xyz-x'z+4x'z-xyz
=x'y-xyz+3x'z
=4*(-3)-2*3*1+3*4*1
=-12-6+12
=-6

8、(5a^2-3b^2)+(a^2+b^2)-(5a^2+3b^2),其中a=-1,b=1
=5a^2-3b^2+a^2+b^2-5a^2-3b^2
=a^2-5b^2
=(-1)^2-5*1^2
=1-5
=-4

9、2(a^2b+ab^2)-2(a^2 b-1)-2ab^2 -2其中a=-2,b=2
=2a^2b+2ab^2-2a^2b+2-2ab^2-2
=0

10、(X-2分之1Y-1)(X-2分之1Y+1)-(X-2分之1Y-1)的平方
其中X=1.7,Y=3.9(先化简再求值)
[(X-2分之1Y)-1][(X+2分之1Y)+1]-(X-2分之1Y-1)平方
=(X+2分之1Y)平方-1-(X-2分之1Y)平方+2(X-2分之1Y)-1
=(X+2分之1Y)平方-(X-2分之1Y)平方+2(X-2分之1Y)-2
=2XY+2X-Y-2
=3.9*2.4+1.4
=10.76

Answer 2

1、已知A,B是方程x^2+2x-5=0的两个实数根,
求(A^2+2AB+2A)(B^2+2AB+2B)的值.
由A,B是方程x^2+2x-5=0的两个实数根得：
AB=-5，A+B=-2
A^2+2AB+2A)(B^2+2AB+2B)
=AB（A+2B+2）（B+2A+2）
=-5（-2+B+2）（-2+A+2）
=-5AB
=25
2、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y),其中x-y=6,xy=21.要详细步骤
化简得：
1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y)=
1/2[(x+y)方+2z(x+y)+z方]+1/2[(x-y)方-z方]-z(x+y)=
1/2(x+y)方+1/2(x-y)方=x方＋y方
由x-y=6,xy=21得，x方＋y方＝（x-y）方＋2xy＝78
3、a^2-ab+2b^2=3 求2ab-2a^2-4b^2-7的值
2ab-2a^2-4b^2-7
=2(ab-a^2-2b^2)-7
=-2(a^2-ab+2b^2)-7
=(-2)*3-7
=-6-7=-13
4、若A=2x^2+3xy-2x-3,B=-x^2+xy+2,且3A+6B的值与x无关，求y的值

3A+6B=6x^2+9xy-6x-9-6x^2+6xy+12
=15xy-6x+3
=x(15y-6)+3
5、9x+6x^2 -3(x-2/3x^2).其中x=-2
9x+6x² -3(x-2/3x²)
=9x+6x²-3x+2x²
=8x²+6x
=8×(-2)²+6×(-2)
=32-12
=20

Answer 3

2(2a²+2ab)-(3a²+4ab-b²）,其中a=2,b=-1
1/4（a+b）²-6(a-b)+3/4(a+b)²+6(a-b)
5（a-b）²-3(a-b)²-7(a-b)-(a-b)²+7(a-b)
1/2a²-1/4b+3/2a²-3/4b-a²
-5yx²+4xy²-2xy+6x²y+2xy+5
16m+25-40m+34m
(4+2x)+(2x-x)
4a+8a-(-6a)+3a-2b
8a+4(a+2)
(2n-3)+(2n+3)-(2n-3)
7x-(5x-5y)-y
3a-4b+4a-3b
7a+3b-(4a+5b)-3
3ab-4ab+8ab-7ab+ab
(x-y)-2(x-y)
.16m+25-40m+34m
.(4+2x)+(2x-x)
4a+8a-(-6a)+3a-2b
.8a+4(a+2)
(2n-3)+(2n+3)-(2n-3)
7x-(5x-5y)-y
3a-4b+4a-3b
.7a+3b-(4a+5b)-3
3ab-4ab+8ab-7ab+ab
.(x-y)-2(x-y)
x-[y-2x-(x+y)]
3ab-4ab+8ab-7ab+ab
7x-(5x-5y)-y
23a3bc2-15ab2c+8abc-24a3bc2-8abc
-7x2+6x+13x2-4x-5x2
2y+(-2y+5)-(3y+2)
(2x2-3xy+4y2)+(x2+2xy-3y2)
2a-(3a-2b+2)+(3a-4b-1)
-6x2-7x2+15x2-2x2
2x-(x+3y)-(-x-y)-(x-y)
2x+2y-[3x-2(x-y)]
5-(1-x)-1-(x-1)
10x2-xy．
x3-2x2y+4xy2+y3．
4x2-[7x2-5x-3(1-2x+x2)]

Answer 4

哈哈哈哈还是时候

Answer 5

3y十2y-y十y，其中，y=1
解:原式=5y一y十y
=4y十y
=5y
当y=1时
原式=5y
=5x1
=5