I am working on the following. A point charge of √3Q is at point (3a, a, 2a) Find charge at (2a, 2a, 3a) I'm using Coulomb's Law E(r) = q / 4∏ε0 (r-r0)3 (lr-r0l & can get through most of it, but looking at my book I can't see why the last step occurs. See attachment. I can find r-ro & its magnitude lr-r0l as well, so can sub into the equation. r = (2a, 2a, 3a) r0 = (2a, 2a, 3a) r-r0 = (-a, a, a) lr-r0l = √ -1)2 +1)2 +1)2 = √3 E(r) = √3q / 4∏ε0 (3a)3 (-a, a, a) Then the answer is E(r) = q / 4∏ε0 (√3)2 (-?a, ?a, ?a) How do you change this, mathematically, from the line above? Can't see the wood for trees again, I expect, but I need a bit of a memory jog, please.