x1x2是方程x²-2x+a=0的两个实数根,且x1+2x2=3-根号21求x1,x2及a的值 2求x1³-3_数学解答

x1x2是方程x²-2x+a=0的两个实数根,且x1+2x2=3-根号2
1求x1,x2及a的值 2求x1³-3x1²+2x1+x2的值

人气：444 ℃　时间：2019-10-19 18:06:55

解答

1、
x1+x2=2
x1+2x2=3-√2
所以x2=3-√2-2=1-√2
x1=2-x2=2-1+√2=1+√2
a=x1x2=(1-√2)(1+√2)=1-2=-1
2、
x1³-3x1²+2x1+x2
=x1(x1²-3x1+2)+x2
=x1(x1-1)(x1-2)+x2
=(1+√2)(√2)(-1+√2)+1-√2
=√2+1-√2
=1