1.若x^2+2x=3,则x^4+7x^3+8x^2-13x+15=2.已知当a=-2时,代数式ax^3+bx+1的值为3,那么当x=2时,ax^3+bx-2=3.设m和n均不为0,3x^2y^3和-6x^(2+2m+n)y^3是同类项,则2m^3-3m^2n+mn^2+7n^3/4m^3+2m^2n-5mn^2+7n^3=4.当m=2π时,多项式am^3+bm+1

1.若x^2+2x=3,则x^4+7x^3+8x^2-13x+15=2.已知当a=-2时,代数式ax^3+bx+1的值为3,那么当x=2时,ax^3+bx-2=3.设m和n均不为0,3x^2y^3和-6x^(2+2m+n)y^3是同类项,则2m^3-3m^2n+mn^2+7n^3/4m^3+2m^2n-5mn^2+7n^3=4.当m=2π时,多项式am^3+bm+1
1.若x^2+2x=3,则x^4+7x^3+8x^2-13x+15=
2.已知当a=-2时,代数式ax^3+bx+1的值为3,那么当x=2时,ax^3+bx-2=
3.设m和n均不为0,3x^2y^3和-6x^(2+2m+n)y^3是同类项,则2m^3-3m^2n+mn^2+7n^3/4m^3+2m^2n-5mn^2+7n^3=
4.当m=2π时,多项式am^3+bm+1的值是0,则多项式4aπ^3+bπ+5.5=
5.若a+b+c=30,3a+b-c=50,b、c均为非负数,试求x=5a+4b+2c的取值范围.
6.已知多项式x^2+ax-y+b和bx^2-3x+6y-3的差的值与字母x的取值无关,求代数式3（a^2-2ab-b^2)-2(2a^2-ab+b^2)的值.
急啊…………………………

1.若x^2+2x=3,则x^4+7x^3+8x^2-13x+15=2.已知当a=-2时,代数式ax^3+bx+1的值为3,那么当x=2时,ax^3+bx-2=3.设m和n均不为0,3x^2y^3和-6x^(2+2m+n)y^3是同类项,则2m^3-3m^2n+mn^2+7n^3/4m^3+2m^2n-5mn^2+7n^3=4.当m=2π时,多项式am^3+bm+1
1.若x^2+2x=3,
则x^4+7x^3+8x^2-13x+15
=x^2(x^2+2)+7x(x^2+2)-27x+15
=3x^2+21x-27x+15
=3(x^2-2x+5)
=3(x^2+2x-4x+5)
=3(8-4x)
=12(2-x)
2.已知当a=-2时,代数式ax^3+bx+1的值为3,那么当x=2时,
ax^3+bx-2
=ax^3+bx+1-3
=3-3
=0 .

1.)∵x^2+2x=3
∴x^2+2x+1=3+1
( x+1)² =4
∴x+1= ±2 ∴ x=1或者x=-3
当x=1时,
x^4+7x^3+8x^2-13x+15
=1+7+8-13+15=18
当x=-3
x^4+7x^3+8x^2-13x+15
=81+7×(-27)+72+13×...

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1.)∵x^2+2x=3
∴x^2+2x+1=3+1
( x+1)² =4
∴x+1= ±2 ∴ x=1或者x=-3
当x=1时,
x^4+7x^3+8x^2-13x+15
=1+7+8-13+15=18
当x=-3
x^4+7x^3+8x^2-13x+15
=81+7×(-27)+72+13×3+15=18
2.)∵a=-2时，代数式ax^3+bx+1的值为3
∴ax^3+bx+1-3=3-3
ax^3+bx-2=0
3.)当m=2π时,am^3+bm+1=8a*π^3+2bπ+1=0,两边同时除2，既得4aπ^3+bπ+5.5=0
4.)因为3x^2y^3和-6x^(2+2m+n)y^3是同类项，故x的系数相等，则2=2+2m+n，即n=-2m,带入得2m^3-3m^2n+mn^2+7n^3/4m^3+2m^2n-5mn^2+7n^3=-54m^3+2m^3-16m^3-14=-68m^3-14
5.)a+b+c=30
3a+b-c=50
两式相加得和相减分别得:
b=40-2a≥0,a≤20
c=a-10≥0,a≥10
10≤a≤20
x=5a+4b+2c=5a+4(40-2a)+2(a-10)=140-a
140-a≤140-10=130
140-a≥140-20=120
120≤5a+4b+2c≤130
∴120≤x≤130
6.)已知多项式x^2+ax-y+b和bx^2-3x+6y-3的差的值与字母x的取值无关，
∴x^2+ax-y+b-bx^2+3x-6y+3=(1-b)x^2+(a+3)x-7y+b+3
∴1-b=0 ∴ a+3=0
∴b=1 ∴a=-3
代数式3（a^2-2ab-b^2)-2(2a^2-ab+b^2)
=3a^2-6ab-3b^2-4a^2+2ab-2b^2
=-a^2-4ab-5b^2
=-9+12-5=-2

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