scrie relatiile lui viete
x1+x2+x3+x4= - a3/a4= -1/1=-1
x1x2+x1x3+x1x4+x2x3+x2x4+x3x4= a2/a4=1/1=1
x1x2x3+x1x2x4+x1x3x4+x2x3x4= - a1/a4=-0/1=0
x1x2x3x4=a0/a4=1/1=1
(1-x1)(1-x2)(1-x3)(1-x4)=
=(1-x1-x2+x1x2)(1-x3-x4+x3x4)=
=1-x1-x2-x1x2-x3+x1x3+x2x3-x1x2x3-x4+x1x4+x2x4-x1x2x4+x3x4-x1x3x4-x2x3x4+x1x2x3x4
=1-x1-x2-x3-x4+x1x2+x1x3+x1x4+x2x3+x2x4+x3x4-x1x2x3-x1x2x4-x1x3x4-x2x3x4+x1x2x3x4=
inlocuiesti
=1-(-1)+1-0+1=4
