0,x\in(-\infty;1)\cup(3;\infty)\\f(x)<0,x\in(1;3)" alt="x^2-4x+3\\D=16-12=4\\\left.\begin{array}{cc}x_1=\frac{4+\sqrt4}2=3&x_2=\frac{4-\sqrt4}2=1\end{array}\right.\\f(x)>0,x\in(-\infty;1)\cup(3;\infty)\\f(x)<0,x\in(1;3)" align="absmiddle" class="latex-formula">