1.若x^2+2x=3,则x^4+7x^3+8x^2-13x+15=

题目

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…………………………

答案

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 .