5x^2+3x-9=0
x1/x2+x2/x1=?
Din relatiile lui Viette:
S= x1 + x2 = -b/a= -3/5
P= x1*x2= c/a= -9/5
x1/x2+x2/x1= (x1^2+x2^2)x1x2
Stim ca (x+y)^2= x^2+ y^2+ 2xy => x^2+y^2=(x+y)^2-2xy, atunci: x^2+y^2=s^2-2p
x1^2+x2^2= (-3/5)^2 - 2(-9/5)
x1^2+x2^2= 9/25 + 18/5= 99/25
(x1^2+x2^2)x1x2= 99/25/-9/5= -11/125