- $\mathop {\min }\limits_{\left( {0; + \infty } \right)} f\left( x \right) = 3$
- $\mathop {\min }\limits_{\left( {0; + \infty } \right)} f\left( x \right) = 2$.
- $\mathop {\min }\limits_{\left( {0; + \infty } \right)} f\left( x \right) = - 5$.
- $\mathop {\min }\limits_{\left( {0; + \infty } \right)} f\left( x \right) = - 3$.