I'm a little confused on how the math is supposed to work out when you are adding an electric field from charges with opposite signs. Looking at the image, both of these situations should yield equivalent electric fields at that point right? I get the right answer for when the situation involves two identical charges, but when the charges are opposite i have an extra negative coefficient from the -q which messes up my calculations. I think the problem is that when I draw triangles to try and split up the components that perhaps my Y should be positive for the -q charge, but I'm not sure if/why that should be the case. Otherwise I'm not really sure what I'm doing wrong....any help would be appreciated.