关于因式分解的20道数学题,知道几道回答几道,明天下午要交.

1)x^2-5x-36=(x-9)(x+4)
2)x^2-14x+24=(x-2)(x-12)
3)x^2-2x-8 =(x-4)(x+2)
4)-a^2-3a-2 =-(x+1)(x+2)
5)x^4+x^3+6x^2+5x+5
=(x^4+5x^2)+(x^3+5x)+(x^2+5 )
=(x^2+5 )(x^2+x+1)
6)14(m+n)^2-11(m+n)-15
=[2(m+n)-3][7(m+n)+5]
=(2m+2n-3)(7m+7n+5)
7)x^2-(m+8)x+7(m+1)=(x-7)(x-m-1)
8)x^(n+2)-5x^(n+1)+4x^n
=x^n(x^2-5x+4)
=x^n(x-1)(x-4)
9)x^4-21x^2-100
=(x^2-25)(x^2+4)
10)x^4-3x^3-28x^2
=x^2(x^2-3x-28)
=x^2(x-7)(x+4)
11)(x+1)(x-4)-6
=x^2-3x-10
=(x+2)(x-5)
12)4x^(n+2)-9x^n+6x^(n-1)-x^(n-2)
=4x^(n+2)+6x^(n-1)-9x^n-x^(n-2)
=(4x^4-9x^2+6x-1)x^(n-2)
=(4x^4-4x^2-5x^2+6x-1)x^(n-2)
=[(x+1)(x-1)4x^2-(5x-1)(x-1)]x^(n-2)
=(4x^3+4x^2-5x+1)(x-1)x^(n-2)
=(4x^3-x+4x^2-4x+1)(x-1)x^(n-2)
=[(x(2x+1)(2x-1)+(2x-1)^2](x-1)x^(n-2)
=(2x^2+3x-1)(2x-1)(x-1)x^(n-2)
13)x^2+10x+21 =(x+3)(x+7)
14)令x^2+x=A
原式=（A+1）（A+2）-12
=A^2+3A-10
=(A-2)(A+5)
=(x^2+x-2)(x^2+x+5)
15)4x^2-4ax+a^2-b^2
=[2x-(a+b)][2x-(a-b)]
=(2x-a-b)(2x-a+b)
16)x^4-x^3+x^2+2
=(x^4+2x^2+1)-x^2+(1-x^3)
=(x^2+1)^2-x^2+(1-x)(x^2+x+1)
=(x^2+x+1)(x^2-x+1)+(1-x)(x^2+x+1)
=(x^2+x+1)(x^2-2x+2)
17)x^2-5x(y-1)-6(1-y)^2
=6(y-1)^2 -5x(y-1)+x^2
=[2(y-1)-x][3(y-1)-x]
=(2y-x-2)(3y-x-3)
18)4x^2+2x-9y^2-3y
=(4x^2-9y^2)+(2x-3y)
=(2x+3y)(2x-3y)+(2x-3y)
=(2x-3y)(2x+3y+1)
19)a^2-4ab+4b^2-2ac^2+4bc^2+c^4-1
=(a-2b)^2-2(a-2b)c^2+c^4-1
=(a-2b-c^2)-1
=(a-2b-c^2-1)(a-2b-c^2+1)
20)5+7(a+1)-6(a+1)^2
=[2(a+1)+1][-3(a+1)+5]
=(2a+3)(2-3a)
问题补充
1）x^5+x+1
＝x^5-x^2+x^2+x+1
=x^2(x^3-1)+(x^2+x+1)
=(x-1)(x^2+x+1)x^2+(x^2+x+1)
=(x^2+x+1)(x^3-x^2+1)
2)2a^2b^2+2a^2c^2+2b^2c^2-a^4-b^4-c^4
=4a^2b^2-(a^4+b^4+c^4+2a^2b^2-2a^2c^2-2b^2c^2)
=(2ab)^2-(a^2+b^2-c^2)^2
=(2ab+a^2+b^2-c^2)(2ab-a^2-b^2+c^2)
=[(a+b)^2-c^2][c^2-(a-b)^2]
=(a+b-c)(a+b+c)(c+a-b)(c-a+b)
3）(x^2+3x)^2-2(x^2+3x)-8
=[(x^2+3x)-4][(x^2+3x)+2]
=(x^2+3x-4)(x^2+3x+2)
4)(x-1)(x-4)(x-3)(x-2)-120
=(x^2-5x+4)(x^2-5x+6)-120
令x^2-5x=A
原式=(A+4)(A+6)-120
=A^2+10A-96
=(A-6)(A+16)
=(x^2-5x-6)(x^2-5x+16)
5)4x^2-4x-y^2+4y-3
=4x^2-4x+1-y^2+4y-4
=(2x-1)^2-(y^2-4y+4)
=(2x-1)^2-(y-2)^2
=(2x-1+y-2)(2x-1-y+2)
=(2x+y-3)(2x-y+1)
6)2x^2-5xy+x-3y^2+11y-6
=2x^2+(1-5y)x-(y-3)(3y-2)
=[x-(3y-2)][2x+(y-3)]
=(x-3y+2)(2x+y-3)

1. (x+4)(x-9)
2. (x-2)(x-12)
3. (x+2)(x-4)
4. (-a-2)(a+1)
5. (x^2+x+1)(x^2+5)
6. (7m+7n+5)(2m+2n-3)
7. (x-7)(x-m-1)
8. x^n(x-1)(x-4)
9. (x-5)(x+5)(x^2+4)
10. x^2(x-...

1.（X-9）*（X+4）
2.（X-2）*（X-12）
3.（X-4）*（X+2）

1.（X-9）*（X+4）
2.（X-2）*（X-12）
3.（X-4）*（X+2）
4.-（a+1）*(a+2)
5.
6.(2m+2n-3)*(7m+7n+5)
7.(X-7)*(X-m-8)
8.x^n（X-4）*(X-1)
9.(x^2-25）*（x^2+4）
10.x^2（x-7）*（x+4）
11.（x-5...