If f {\displaystyle f} is defined on the closed interval [ − 1 , 1 ] {\displaystyle [-1,1]} , then f {\displaystyle f} attains a global maximum on that interval.
![{\displaystyle [-1,1]}](https://wiki.ubc.ca/api/rest_v1/media/math/render/svg/51e3b7f14a6f70e614728c583409a0b9a8b9de01)