如果x2+x-1=0那么代数式x3+2x-7的值为

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如果x2+x-1=0那么代数式x3+2x-7的值为如果x2+x-1=0那么代数式x3+2x-7的值为如果x2+x-1=0那么代数式x3+2x-7的值为x3-2x-7=x3+x2-x2+2x-7=(x3

如果x2+x-1=0那么代数式x3+2x-7的值为
如果x2+x-1=0那么代数式x3+2x-7的值为

如果x2+x-1=0那么代数式x3+2x-7的值为
x3-2x-7
=x3+x2-x2+2x-7
=(x3+x2-x)-(x2+x-1)-8
=x(x2+x-1)-(x2+x-1)-8
=-8

X2+X-1=0
X2+X=1 X3+X2=X
X3=X-X2
X3-2X-7
=X-X2-2X-7
=-(X2+X)-7
=-8

1.x3-2x-7
=x3+x2-x2+2x-7
=(x3+x2-x)-(x2+x-1)-8
=x(x2+x-1)-(x2+x-1)-8
=-8
2.X2+X-1=0
X2+X=1 X3+X2=X
X3=X-X2
X3-2X-7
=X-X2-2X-7
=-(X2+X)-7
=-8