Not quite getting this trig stuff

hi guys.

currently studying some maths at university, and they assume a whole bunch of high school maths knowledge. problem is, i was at high school 7 years ago, i've forgotten it all.

anyway....

I'm having some trouble working these kind of problems out...

tan x = 1

i would love to reach for my calculator and get 0.785398, but unfortunately the kind of answer i need is pi/4 ....

I've been staring at unit circles and triangles and stuff trying to work them out, but i'm just not getting it. how do i answer these kind of problems without reaching for the calculator?

Thanks in advance for any help, exam is tomorrow, and boy do i need it!!