函数$f\left(x\right)={\cos }^{2}x-\frac{1}{2}$的最小正周期为（ ）

根据短文内容完成下列各题

    Today l would like to tell you about my dream．

    My dream is a simple but great one．It is to be a teacher．①我从小就梦想做一名老师!②First of all，it is a pleasure for me to be with children．They make me feel ③ happy and young．Furthermore，teachers play an important part in the development of children．They teach children and show them how to be good．When children grow up，they use the knowledge that they have learned to develop their motherland and make it beautiful. I think teaching is one of the ④    (value) things in the world．

    That’s all．Thank you !