I'm having trouble with this question

$\displaystyle Let\ f\ be\ continuous\ on\ \Re\ with\ \lim{x \rightarrow \inf} = \lim{x \rightarrow -\inf} = 0$

$\displaystyle 1)\ Give\ an\ example\ of$ $\displaystyle such\ a\ function\ which\ has$ $\displaystyle both\ a\ maximum\ value\ and\ a\ minimum\ value.$

$\displaystyle 2)\ Given\ an\ example\ of$ $\displaystyle such\ a\ function\ which\ has\ a$ $\displaystyle minimum\ value\ but\ no\ maximum\ value.$

$\displaystyle 3)\ Show\ that\ if\ there\ is\ a$ $\displaystyle number\ \xi\ such\ that\ f(\xi)>0$ $\displaystyle then\ f\ attains\ a\ maximum\ value\ on\ \Re.$