Question

数学，初三，3个问题，要详细过程！定好评！

Answer 1

1.  x^2-2x-1=0   x1+x2=2     x1x2=-1

   (x1-1)(x2-1)=x1x2-x1-x2+1=x1x2-(x1+x2)+1=-1-2+1=-2

2. x^2-5x+c=0     x1=2

   4-10+c=0    c=6

   x^2-5x+6=0    

   x1+x2=5  x2=3

   x2=3    c=6

3. 2x^2-x-2=0

   x1+x2=1/2      x1x2=-1

   x1^2+x2^2=(x1+x2)^2-2x1x2=(1/2)^2+2=9/4

   1/x1+1/x2=(x2+x1)/x1x2=1/2/-1=-1/2

   (x1-x2)^2=x1^2-2x1x2+x2^2=9/4+2=17/4