Please need help with min and max of wave?!

Hi guys i need to find the min and max values of this wave and i have no idea how to do so, any help is much appreciated thanks! :)

[Jan]

We will not solve your homework. We cannot guess, if you worked with symbolic computations in your lesson or if calculating the gradient numerically is the topic of your lessons currently. So I suggest to show, what you have tried so far.

[Jack]

I have not been taught this yet, I have had 3 matlab lectures and am simply trying to get ahead for my lab later this week.