Question

已知x2+x-1=0 求x3-x2-x+7的值

Answer 1

x3-x2-x+7=x(x^2+x-1)-2x^2+7=-2x^2+7因为x2+x-1=0，所以，x^2=1-x,代入上式得x3-x2-x+7=2x+5x2+x-1=0,解得x=(-1±√5）/2所以x3-x2-x+7=2x+5=4±√5

Answer 2

x3-x2-x+7=x^3 -(x^2 +x-7)=x^3 -(x^2 +x-1-6)=x^3 +6然后解出x^2 +x -1 =0的根 (x+1/2)^2 =5/4 x+1/2 =（根式5）/2 或-(根式5)/2 x1 =[（根式5）-1]/2 x2 =[-(根式5) -1]/2即 x^3 +6=然后代入 就别嫌弃麻烦了 大致思路就这样吧

Answer 3

x3-x2-x+7=x(x2+x-1)-2x2+7=x*0-2x2+7=7-2x2=7-2(1-x)=5+2x 把X解出代入就出来

Answer 4

解为：