求幾道初一先化簡再求值的題帶答案的,我先自己練練

2021-03-07 04:14:52 字數 9960 閱讀 6809

1樓:網際超人

^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

=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

化間求值: 下面的你自己求吧```

1、-9(x-2)-y(x-5)

(1)化簡整個式子。

(2)當x=5時,求y的解。

2、5(9+a)×b-5(5+b)×a

(1)化簡整個式子。

(2)當a=5/7時,求式子的值。

3、62g+62(g+b)-b

(1)化簡整個式子。

(2)當g=5/7時,求b的解。

4、3(x+y)-5(4+x)+2y

(1)化簡整個式子。

5、(x+y)(x-y)

(1)化簡整個式子。

6、2ab+a×a-b

(1)化簡整個式子。

7、5.6x+4(x+y)-y

(1)化簡整個式子。

8、6.4(x+2.9)-y+2(x-y)

(1)化簡整個式子。

9、(2.5+x)(5.2+y)

(1)化簡整個式子。

10、9.77x-(5-a)x+2a

(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

=-42(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 x+7-(-36+8^2)/2=[-(-8x)+7^4]/3*(8^2-6x)

(a-7)-(-98a)+7a=[(3.2*5a)2^5]/10

(89/2+5x)+35/6x=[3*(-9+5)+2^3]/5+7x

[3x+(-189+5^2)/3]/8=521/2

4y+[119*(-5^3y+8/7)-8/3]=22/11

(3x*189)+

7(2x-1)-3(4x-1)=4(3x+2)-1

(5y+1)+ (1-y)= (9y+1)+ (1-3y)

[-6(-7^4*8)-4]=x+2

20%+(1-20%)(320-x)=320×40%

2(x-2)+2=x+1

2(x-2)-3(4x-1)=9(1-x)

11x+64-2x=100-9x

15-(8-5x)=7x+(4-3x)

3(x-7)-2[9-4(2-x)]=22

3/2[2/3(1/4x-1)-2]-x=2

2x+7^2=157

9x+6x² -3(x-2/3x²)

=9x+6x²-3x+2x²

=8x²+6x

=8×(-2)²+6×(-2)

=32-12

=201/4(-4x²+2x-8)-(1/2x-1)

=-x²+1/2x-2-1/2x+1

=-x²-1

=-(1/2)²-1

=-1/4-1

=-5/4

3.3ab-4ab+8ab-7ab+ab=______.

4.7x-(5x-5y)-y=______.

5.23a3bc2-15ab2c+8abc-24a3bc2-8abc=______.

6.-7x2+6x+13x2-4x-5x2=______.

7.2y+(-2y+5)-(3y+2)=______.

11.(2x2-3xy+4y2)+(x2+2xy-3y2)=______.

12.2a-(3a-2b+2)+(3a-4b-1)=______.

13.-6x2-7x2+15x2-2x2=______.

14.2x-(x+3y)-(-x-y)-(x-y)=______.

16.2x+2y-[3x-2(x-y)]=______.

17.5-(1-x)-1-(x-1)=______.

18.( )+(4xy+7x2-y2)=10x2-xy.

19.(4xy2-2x2y)-( )=x3-2x2y+4xy2+y3.

21.已知a=x3-2x2+x-4,b=2x3-5x+3,計算a+b=______.

22.已知a=x3-2x2+x-4,b=2x3-5x+3,計算a-b=______.

23.若a=-0.2,b=0.5,代數式-(|a2b|-|ab2|)的值為______.

25.一個多項式減去3m4-m3-2m+5得-2m4-3m3-2m2-1,那麼這個多項式等於______.

26.-(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=______.

(二)選擇

[ ]a.2;

b.-2;

c.-10;

d.-6.

52.下列各式中計算結果為-7x-5x2+6x3的是 [ ]

a.3x-(5x2+6x3-10x);

b.3x-(5x2+6x3+10x);

c.3x-(5x2-6x3+10x);

d.3x-(5x2-6x3-10x).

53.把(-x-y)+3(x+y)-5(x+y)合併同類項得 [ ]

a.(x-y)-2(x+y);

b.-3(x+y);

c.(-x-y)-2(x+y);

d.3(x+y).

54.2a-[3b-5a-(2a-7b)]等於 [ ]

a.-7a+10b;

b.5a+4b;

c.-a-4b;

d.9a-10b.

55.減去-3m等於5m2-3m-5的代數式是 [ ]

a.5(m2-1);

b.5m2-6m-5;

c.5(m2+1);

d.-(5m2+6m-5).

56.將多項式2ab-9a2-5ab-4a2中的同類項分別結合在一起,應為 [ ]

a.(9a2-4a2)+(-2ab-5ab);

b.(9a2+4a2)-(2ab-5ab);

c.(9a2-4a2)-(2ab+5ab);

d.(9a2-4a2)+(2ab-5ab).

57.當a=2,b=1時,-a2b+3ba2-(-2a2b)等於 [ ]

a.20;

b.24;

c.0;

d.16.

中,正確的選擇是 [ ]

a.沒有同類項;

b.(2)與(4)是同類項;

c.(2)與(5)是同類項;

d.(2)與(4)不是同類項.

59.若a和b均為五次多項式,則a-b一定是 [ ]

a.十次多項式;

b.零次多項式;

c.次數不高於五次的多項式;

d.次數低於五次的多項式.

60.-{[-(x+y)]}+{-[(x+y)]}等於 [ ]

a.0;

b.-2y;

c.x+y;

d.-2x-2y.

61.若a=3x2-5x+2,b=3x2-5x+6,則a與b的大小是

[ ]a.a>b;

b.a=b;

c.a<b;

d.無法確定.

62.當m=-1時,-2m2-[-4m2+(-m2)]等於 [ ]

a.-7;

b.3;

c.1;

d.2.

63.當m=2,n=1時,多項式-m-[-(2m-3n)]+[-(-3m)-4n]等於 [ ]

a.1;

b.9;

c.3;

d.5.

[ ]65.-5an-an-(-7an)+(-3an)等於 [ ]

a.-16an;

b.-16;

c.-2an;

d.-2.

66.(5a-3b)-3(a2-2b)等於 [ ]

a.3a2+5a+3b;

b.2a2+3b;

c.2a3-b2;

d.-3a2+5a-5b.

67.x3-5x2-4x+9等於 [ ]

a.(x3-5x2)-(-4x+9);

b.x3-5x2-(4x+9);

c.-(-x3+5x2)-(4x-9);

d.x3+9-(5x2-4x).

[ ]69.4x2y-5xy2的結果應為 [ ]

a.-x2y;

b.-1;

c.-x2y2;

d.以上答案都不對.

(三)化簡

70.(4x2-8x+5)-(x3+3x2-6x+2).

72.(0.3x3-x2y+xy2-y3)-(-0.5x3-x2y+0.3xy2).

73.-{2a2b-[3abc-(4ab2-a2b)]}.

74.(5a2b+3a2b2-ab2)-(-2ab2+3a2b2+a2b).

75.(x2-2y2-z2)-(-y2+3x2-z2)+(5x2-y2+2z2).

76.(3a6-a4+2a5-4a3-1)-(2-a+a3-a5-a4).

77.(4a-2b-c)-5a-[8b-2c-(a+b)].

78.(2m-3n)-(3m-2n)+(5n+m).

79.(3a2-4ab-5b2)-(2b2-5a2+2ab)-(-6ab).

80.xy-(2xy-3z)+(3xy-4z).

81.(-3x3+2x2-5x+1)-(5-6x-x2+x3).

83.3x-(2x-4y-6x)+3(-2z+2y).

84.(-x2+4+3x4-x3)-(x2+2x-x4-5).

85.若a=5a2-2ab+3b2,b=-2b2+3ab-a2,計算a+b.

86.已知a=3a2-5a-12,b=2a2+3a-4,求2(a-b).

87.2m-{-3n+[-4m-(3m-n)]}.

88.5m2n+(-2m2n)+2mn2-(+m2n).

89.4(x-y+z)-2(x+y-z)-3(-x-y-z).

90.2(x2-2xy+y2-3)+(-x2+y2)-(x2+2xy+y2).

92.2(a2-ab-b2)-3(4a-2b)+2(7a2-4ab+b2).

94.4x-2(x-3)-3[x-3(4-2x)+8].

(四)將下列各式先化簡,再求值

97.已知a+b=2,a-b=-1,求3(a+b)2(a-b)2-5(a+b)2×(a-b)2的值.

98.已知a=a2+2b2-3c2,b=-b2-2c2+3a2,c=c2+2a2-3b2,求(a-b)+c.

99.求(3x2y-2xy2)-(xy2-2x2y),其中x=-1,y=2.

101.已知|x+1|+(y-2)2=0,求代數式5(2x-y)-3(x-4y)的值.

106.當p=a2+2ab+b2,q=a2-2ab-b2時,求p-[q-2p-(p-q)].

107.求2x2-{-3x+5+[4x2-(3x2-x-1)]}的值,其中x=-3.

110.當x=-2,y=-1,z=3時,求5xyz-{2x2y-[3xyz-(4xy2-x2y)]}的值.

113.已知a=x3-5x2,b=x2-6x+3,求a-3(-2b).

(五)綜合練習

115.去括號:{-[-(a+b)]}-{-[-(a-b)]}.

116.去括號:-[-(-x)-y]-[+(-y)-(+x)].

117.已知a=x3+6x-9,b=-x3-2x2+4x-6,計算2a-3b,並把結果放在前面帶「-」號的括號內.

118.計算下式,並把結果放在前面帶「-」號的括號內:

(-7y2)+(-4y)-(-y2)-(+5y)+(-8y2)+(+3y).

119.去括號、合併同類項,將結果按x的升冪排列,並把後三項放在帶有「-」號的括號內:

120.不改變下式的值,將其中各括號前的符號都變成相反的符號:(x3+3x2)-(3x2y-7xy)+(2y3-3y2).

121.把多項式4x2y-2xy2+4xy+6-x2y2+x3-y2的三次項放在前面帶有「-」號的括號內,二次項放在前面帶有「+」號的括號內,四次項和常數項放在前面帶有「-」號的括號內.

122.把下列多項式的括號去掉,合併同類項,並將其各項放在前面帶有「-」號的括號內,再求2x-2[3x-(5x2-2x+1)]-4x2的值,其中x=-1.

123.合併同類項:

7x-1.3z-4.7-3.2x-y+2.1z+5-0.1y.

124.合併同類項:5m2n+5mn2-mn+3m2n-6mn2-8mn.

126.去括號,合併同類項:

(1)(m+1)-(-n+m);

(2)4m-[5m-(2m-1)].

127.化簡:2x2-{-3x-[4x2-(3x2-x)+(x-x2)]}.

128.化簡:-(7x-y-2z)-{[4x-(x-y-z)-3x+z]-x}.

129.計算:(+3a)+(-5a)+(-7a)+(-31a)-(+4a)-(-8a).

130.化簡:a3-(a2-a)+(a2-a+1)-(1-a4+a3).

131.將x2-8x+2x3-13x2-2x-2x3+3先合併同類項,再求值,其中x=-4.

132.在括號內填上適當的項:[( )-9y+( )]+2y2+3y-4=11y2-( )+13.

133.在括號內填上適當的項:

(-x+y+z)(x+y-z)=[y-( )][y+( )].

134.在括號內填上適當的項:

(3x2+xy-7y2)-( )=y2-2xy-x2.

135.在括號內填上適當的項:

(1)x2-xy+y-1=x2-( );

(2)[( )+6x-7]-[4x2+( )-( )]=x2-2x+1.

136.計算4x2-3[x+4(1-x)-x2]-2(4x2-1)的值.

137.化簡:

138.用豎式計算

(-x+5+2x4-6x3)-(3x4+2x2-3x3-7).

139.已知a=11x3+8x2-6x+2,b=7x3-x2+x+3,求2(3a-2b).

140.已知a=x3-5x2,b=x3-11x+6,c=4x-3,求

(1)a-b-c;

(2)(a-b-c)-(a-b+c).

141.已知a=3x2-4x3,b=x3-5x2+2,計算

(1)a+b;

(2)b-a.

142.已知x<-4,化簡|-x|+|x+4|-|x-4|.

146.求兩代數式-1.56a+3.2a3-0.

47,2.27a3-0.02a2+4.

03a+0.53的差與6-0.15a+3.

24a2+5.07a3的和.

-0.3,y=-0.2.

150.已知(x-3)2+|y+1|+z2=0,求x2-2xy-5x2+12xz+3xy-z2-8xz-2x2的值.

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