M4 relative motion

I fail to understand this chapter.
My teacher keeps using triangles and stuff with trig.but this doesnt make sence to me and all i can think of is changing everything to i and j.form :/
And like when it comes.to some questions my intuitive understanding of relative motion goes out the window lol

This chapter is in my opinion one of the hardest in Mechanics!!

Im not sure whats wrong with splitting everything into x and y components of velocity..