初一給我出50道化簡求值題,順便寫上答案。謝謝

2021-03-07 04:14:52 字數 5669 閱讀 4197

1樓:匿名使用者

^(3x+2y)+(4x+3y)其中x=5,y+3

解:原式=3x+2y+4x+3y=7x+5y

當x=5,y=3時

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

=-43.2(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

=01、已知a,b是方程x^2+2x-5=0的兩個實數根,

求(a^2+2ab+2a)(b^2+2ab+2b)的值.

由a,b是方程x^2+2x-5=0的兩個實數根得:

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

=252、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y),其中x-y=6,xy=21.要詳細步驟

化簡得:

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的值與x無關,求y的值

解: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

=206、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

=-68、(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

=-49、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

=010、(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(先化簡再求值)

[(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

1、已知a,b是方程x^2+2x-5=0的兩個實數根,

求(a^2+2ab+2a)(b^2+2ab+2b)的值.

由a,b是方程x^2+2x-5=0的兩個實數根得:

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

=252、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y),其中x-y=6,xy=21.要詳細步驟

化簡得:

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的值與x無關,求y的值

解: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

=206、1/4(-4x^2+2x-8)-(1/2x-1),其中x=1/2

1/4(-4x²+2x-8)-(1/2x-1)

=-x²+1/2x-2-1/2x+1

=-x²-1

=-(1/2)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

=-68、(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

=-49、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

=010、(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(先化簡再求值)

[(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

11.(3x+2y)+(4x+3y)其中x=5,y+3

解:原式=3x+2y+4x+3y=7x+5y

當x=5,y=3時

原式=5*7+(-3)*5+20

12.(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

=-413.2(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

=014.2a-(3a-2b+2)+(3a-4b-1) =(     ),a=b=1

=2a-3a+2b-2+3a-4b-1

=(2-3+3)a+(2-4)b+(-2-1)

=2a-2b-3=-3

15.5-(1-x)-1-(x-1),x=11

=5-1+x-1-x+1

=4③2x-(x+3y)-(-x-y)-(x-y)=(    )

=2x-x+3y+x+y-x+y

=x+5y

a=2,b=4

求2(a-b-54)+3(a+b)

=5a+b-108

=5*2+4-108

=-94

a=b=1

求a+b-2(a-b+1)

=-a+3b-2

=-1+3-2

=026.-(2x2-y2)-[2y2-(x2+2xy)]=______.

27.若-3a3b2與5ax-1by+2是同類項,則x=______,y=______.

28.(-y+6+3y4-y3)-(2y2-3y3+y4-7)=______.

29.化簡代數式4x2-[7x2-5x-3(1-2x+x2)]的結果是______.

30.2a-b2+c-d3=2a+( )-d3=2a-d3-( )=c-( ).

31.3a-(2a-3b)+3(a-2b)-b=______.

32.化簡代數式x-[y-2x-(x+y)]等於______.

33.[5a2+( )a-7]+[( )a2-4a+( )]=a2+2a+1.

34.3x-[y-(2x+y)]=______.

35.化簡|1-x+y|-|x-y|(其中x<0,y>0)等於______.

36.已知x≤y,x+y-|x-y|=______.

37.已知x<0,y<0,化簡|x+y|-|5-x-y|=______.

38.4a2n-an-(3an-2a2n)=______.

39.若一個多項式加上-3x2y+2x2-3xy-4得

2x2y+3xy2-x2+2xy,

則這個多項式為______.

40.-5xm-xm-(-7xm)+(-3xm)=______.

41.當a=-1,b=-2時,

[a-(b-c)]-[-b-(-c-a)]=______.

43.當a=-1,b=1,c=-1時,

-[b-2(-5a)]-(-3b+5c)=______.

44.-2(3x+z)-(-6x)+(-5y+3z)=______.

45.-5an-an+1-(-7an+1)+(-3an)=______.

46.3a-(2a-4b-6c)+3(-2c+2b)=______.

48.9a2+[7a2-2a-(-a2+3a)]=______.

50.當2y-x=5時,5(x-2y)2-3(-x+2y)-100=______.

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