1.k≠0
△>0
△=(2k-1)²-4*2k*(2/1k)>0
=4k²-4k+1-16>0
=k²-k-15>0
(2k+3)(2k-5)>0
k>2/5或k<-2/3
2.3x^2-5x-1=0
X1+X2=5/3
X1*X2=-1/3
x1^2+x2^2=(X1+X2)²-2X1*X2=31/9
x2/x1+x1/x2=(X1²+X2²)/X1X2=-31/3
1.k≠0
△>0
△=(2k-1)²-4*2k*(2/1k)>0
=4k²-4k+1-16>0
=k²-k-15>0
(2k+3)(2k-5)>0
k>2/5或k<-2/3
2.3x^2-5x-1=0
X1+X2=5/3
X1*X2=-1/3
x1^2+x2^2=(X1+X2)²-2X1*X2=31/9
x2/x1+x1/x2=(X1²+X2²)/X1X2=-31/3