Hi, I'm reading through one of my books and it's explaining how a vector is eqaul to multiplying sin[itex]\phi[/itex] and [itex]\Delta\vartheta[/itex]. the way it's written in the text is as followed, |[itex]\Delta[/itex]i| [itex]\approx[/itex] (sin[itex]\phi[/itex])[itex]\Delta[/itex][itex]\vartheta[/itex] I have never understood how things like this work. Could someone please explain to me why this is true and how it works? I included a picture of the figure it uses. Thank you.