x1+x2=4x1*x2=2 1/x1+1/x2=(x1+x2)/x1*x2=4/2=2 1/x1*1/x2=1/x1*x2=1/2 方程：x²-2x+1/2=0
设x1,x2是方程x²-4x+2=0的根得 x1+x2=4, x1·x2=2∴1/x1+1/x2=(x1+x2)/x1·x2=4÷2=21/x1×1/x2=1/(x1·x2)=1/2∴新的方程是y²-2y+1/2=0
