[tex]19.\\y=3x^2\\a=3,\ b=0,\ c=0\\\\\dfrac{-b}{2a}=\dfrac{-0}{2(3)=0\to x=0\\\\3x^2=0\ \ \ \ |:3\\\\x^2=0\to x=0[/tex]
[tex]20.\\y=x^2-x-2\\a=1,\ b=-1,\ c=-2\\\\\dfrac{-b}{2a}=\dfrac{-(-1)}{2(1)}=\dfrac{1}{2}\to x=\dfrac{1}{2}\\\\x^2-x-2=0\\\\x^2-2x+x-2=0\\\\x(x-2)+1(x-2)=0\\\\(x-2)(x+1)=0\iff x-2=0\ \vee\ x+1=0\\\\x=2\ \vee\ x=-1[/tex]
