第1个回答 2014-05-20
X1,X2为方程x�0�5+3x+1=0的两根
那么 x1�0�5+3x1+1=0
x1�0�5=-3x1-1
x1(-3x1-1)+8x2+20
=-3x1�0�5-x1+8x2+20
=-3(-3x1-1)-x1+8x2+20
=8(x1+x2)+23
=8×(-3) +23
=-1
第2个回答 2014-05-20
x^2+3x+1=0x1+x2=-3,x1x2=1,x1^2=-3x1-1x1^3+8x2+20=x1*(-3x1-1)+8x2+20=-3x1^2-x1+8x2+20=-3(-3x1-1)-x1+8x2+20=9x1+3-x1+8x2+20=8(x1+x2)+23=-24+23=-1
第3个回答 2014-05-20
X1^2+3X1+1=0(方程的解满足方程)X1^3=X1*X1^2=X1*(-1-3X1)=-X1-3X1^2=-X1-3(-1-3X)=8X1+3X1的3次方+8X2+20=8X1+3+8X2+20=8(X1+X2)+23=-24+23=-1