Can someone please answer this?

Question: I can't understand the red encircled part. Why is it 2d_A²? I think it should be 8d_A² . Also, why did he choose 0.56m and not the other root (4.44 m)?

Q.=+5x10*C Q:=+3x10 C 1 meter In the diagram above, where is the electric field due to the two charges zero?Explanation: Electric eld is a vector. In between the charges is where QA's eld points right and QB's eld points left, so somewhere in between, the two vectors will add to zero. It will be closer to the weaker charge, (23, but since eld depends on the inversesquare of the distance. it will not be linear, and we'll have to do some math. First set the magnitudes of the two elds equal to each other. The vectors point in opposite directions, so when their magnitudes are equal, the vector sum is zero. EA = EB Lg _ L 4od'a-4''od'l isms9 13x10'9 41:0 (1?, ' 4m: (1 an)? i_ 3 (Es _ (1d.-1)2 Many of the terms cancel, making it a bit easier. Now cross multiply and solve the quadratic: 2d10dA+5=0 dA 2 0.56m