Rozhodnite, ktoré z nasledujúcich funkcií nemajú body nespojitosti.
\[ \begin{aligned}
f_1\colon y&=\left\{\begin{array}{lc} x^2 & \text{pre } x\leq 1 \\ 2x & \text{pre } x > 1 \end{array} \right. \\
f_2\colon y& =\left\{ \begin{array}{lc} x^2-2x & \text{pre } x < -1 \\ 3x & \text{pre } x\geq-1 \end{array} \right. \\
f_3\colon y&=\left\{ \begin{array}{lc} 3-x & \text{pre } x\leq 2 \\ (x-1)^2 & \text{pre } x > 2 \end{array} \right. \\
f_4\colon y&=\left\{ \begin{array}{lc}x^2-2x+1& \text{pre } x < 1 \\ \sqrt{x-1} & \text{pre } x\geq1 \end{array} \right.
\end{aligned} \]
Jedinými takými funkciami sú: