Hey guys.. new here.. my precalc hw due 2morro.. with dot products and stuff

Find the Angle theta between the vectors

19: u = <2i-j> v = -2j

21: u = <5i+5j> v=<-6i +6i>

23: u=cos(pi/3)i + sin(pi/3)j v = cos(3pi/4)i + sin(3pi/4)j

PLEASE HELP PRONTO