Im sure this is easy for most of you math wizards, but its really difficult for me to identify which laws and stuff to use and when.

For example:

1)

xarctany

if I want to differentiate that, do I have to use multiplication rule? what would that differentiate out to?

I also have a lot of trouble with radians and points that contain pi. I've never been able to wrap my head around it. if I have the point (-pi/4, 1) and need to plug that point into an equation after ive solved for dy/dx how does it work? if i plug (-pi/4) into say cosin(x) what does it come out to? and whats an easy way to understand this so i can apply it to all trig functions? I just dont get how pi works in this context.

2) How do I find the extreme values (abs and local) of a function? especially one that uses pi in the given range. is there a good online tutorial you could point me to? i dont really want the problem simply done for me i want to try and understand it

Thanks for any help. I really appreciate it as I am struggling here