①已知x²+x-1=0,那么代数式x³+2x²-7的值为_____

①已知x²+x-1=0,那么代数式x³+2x²-7的值为___-6__
x³+2x²-7
=x³+x²-x+x²+x-1-6
=x(x²+x-1)+(x²+x-1)-6
=-6

②已知x²+2x=3,那么x^4+7x³+8x²-13x+15=_18____
x^4+7x³+8x²-13x+15
=x^4+2x³-3x²+5x³+10x²-15x+x²+2x-3+18
=x²(x²+2x-3)+5x(x²+2x-3)+(x²+2x-3)+18
=18