what is the magnitude of the position vector whose terminal point is (-2, 4)?

Vectors always start at the origin and end at the terminal point. Think of it as just a line - the magnitude is the length of the line. So, just find the distance from (0,0) to (-2,4) and that will be the answer.

sqrt(4+16)=sqrt 20 = 2*sqrt5

(x) - (y) = (1 + 4i)

(3 + 6i) - (2 + 2i) = (1 + 4i)