\left \{ {{W(-1)=0} \atop {W(1)=0}} \right.
\left \{ {{a\cdot (-1)^2+b\cdot (-1)+c=0} \atop {a\cdot 1+b\cdot 1+c=0}} \right.
\left \{ {{a-b+c=0} \atop {a+b+c=0}} \right.
dodaję stronami
2a+2c=0 \ |:2
a+c=0
a=-c
podstawiam
a-b+c=0
-c+b+c=0
b=0
\left \{ {{a=-c\Rightarrow c=-a} \atop {b=0}} \right.
{\frac{W(0)}{W(3)}=\frac{a\cdot 0+b\cdot 0+c}{a\cdot 3^2+b\cdot 3+c}=\frac{c}{9a+3b+c}=\frac{c}{9\cdot (-c)+3\cdot 0+c}=\frac{c}{-9c+c}=-\frac{c}{8c}=-\frac{-a}{-8a}=-\frac{1}{8}}