1...a.....xv=(-2)/2*1=-1
yv=-(2^2-4*4*1)/4=-(4-16)/4=-(-12)/4=12/4=3
v(-1;3)
b.......xv=-2/2=-1
yv=-(4-4*(-2))/4=-(4+8)/4=-12/4=-3
v(-1;-3)
2.........xv=-b/2a=>3=-b/2=>6=-b=>b=-6
yv=-delta/4a=-(b*b-4*a*c)/4a=>1=-(36-4c)/4=>4=-36+4c=> 40=4c=>c=10
===>>>>f(x)=x^2-6x+10
