I'm given a bunch of problems for finding the locus and i just need help for a single problem, because this is the question i don't understand from all of them.
Find the locus of points three times as far from (0,4) as from (2,0)
The (0,4) part i understand, you basically expand it three times from its center right? Though i don't get what to do next after that..
I get the impression that you do understand how to do these problems, but are having trouble interpreting what this one says. For that, possibly sketching the concept, as sinx suggested, can be good just as a way to get yourself thinking about the meaning before doing anything mechanical.
It can also be helpful to try paraphrasing the description. Here, you want a point on the locus to be "three times as far from (0,4) as from (2,0)". What does that mean? It means that "the point's distance from (0,4) is three times as far as its distance from (2,0)". So, on one hand, in your sketch you can include not only sinx's point on the line segment, but another point joined to (0,4) and to (2,0), with those segments labeled as, say, 3d and d, respectively. On the other hand, once you have it clear, you can write the (initial) equation easily, using the distance formula.
Another issue is the expected form. You may be expected to go beyond pka's form (the initial equation) to a simplified form, or to a standardized form in which you can recognize it as an ellipse or whatever. (Or the instructions may ask you to describe the locus, rather than give an equation - though I doubt that here.)
If you need more help, you might want to show an example you
were able to do, with your answer, so we can see how this one differs; and be sure to state the exact instructions, so we can be sure what is required.
