[tex]y=- 5x^2+bx+c\\\\a=-5,\ \ x_{1}=4,\ \ x_{2}=-1\\\\stosujemy\ wzory\ Viete'a :\\\\x_{1}+x_{2}= -\frac{b}{a}\\\\4+(-1)=-\frac{b}{-5}\\\\3=\frac{b}{5}\ \ |*5\\\\b=15\\\\\\x_{1}*x_{2}=\frac{c}{a}\\\\4*(-1)=\frac{c}{-5}\\\\-4=\frac{c}{-5}\ \ |*(-5)\\\\c=20\\\\y=-5x^2+15x+20[/tex]
