八年级上数学题

笨 先提公因式

(1) a×b^4÷a^3=b^4÷a^2=(b^2/a)^2
(2) (-x)^6÷（-x）^2×（-x)^3=x^6÷x^2×-x^3=-x
(3) 27x^8÷3x^4 =9x^4=(3x^2)^2
(4) -12m^3n^3÷4m^2n^3=-3m
(5) (6x^2y^3z^2)^2÷4x^3y^4=36x^4y^6z^4÷4x^3y^4=9xy^2z^4
(6）（-6a^2b^5c)÷(-2ab^2)^2=（-6a^2b^5c)÷(4a^2b^4)=-3bc/2
(7) (6a^4-4a^3-2a^2)÷(-2a^2)=2a^2(3a^2-2a-1)÷(-2a^2)=1+2a-3a^2
(8)(4x^3y+6x^2y^2-xy^3)÷2xy=xy(4x^2+6xy-y^2)÷2xy=(4x^2+6xy-y^2)/2
(9)(x^4+2x^3-1/2x^2) ÷(-1/2x)^2=x^2(x^2+2x-1/2)*(4x^2)=x^4(2x^2+4x-1)
(10)(2ab^2-b^3)^2 ÷2b^3 =[b^2(2a-b)]^2÷2b^3=b^4(2a-b)÷2b^3=(2a-b)b/2
(11）｛（x-2y）^2+(x-2y)(x+2y)-2x(2x-y)}÷2x=[x^2-4xy+4y^2+x^2-4y^2-4x^2+2xy]÷2x=[-2x^2-2xy]÷2x=-x-y
分解因式
（1）x^2-25x =(x-25)x
（2) 2x^2y^2-4y^3z =2y^2(x^2-2yz)
(3)am-an+ap=a(m-n+p)
(4)x^3-25x=x(x^2-25)=x(x+5)(x-5)
(5)1-4x^2=(1-2x)(1+2x)
(6) 25x^2+20xy+4y^2=(5x+2y)^2
先化解，再求值：
(1)3a(2a^2-4a+3)-2a^2(3a+4),其中a=-2

3a(2a^2-4a+3)-2a^2(3a+4)=6a^3-12a^2+9a-6a^3-8a^2=a(-20a+9)

其中a=-2,带入等式，a(-20a+9)=-2[-20*（-2）+9]=-98

(2)(a-3b)^2+(3a+b)^2-(a+5b)^2+(a-5b)^2,其中a=-8,b=-6

(a-3b)^2+(3a+b)^2-(a+5b)^2+(a-5b)^2=a^2-6b+9b^2+9a^2+6b+b^2+(a-5b+a+5b)(a-5b-a-5b)=10a^2+10b^2+2a(-10b)=10a^2-20ab+10b^2=10（a-b)^2

其中a=-8,b=-6,带入等式，10（a-b)^2=10(-8+6)=-20.

好辛苦哈哈，只是分数太少了呵呵