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## Homework Statement

two charges, are +10 microcoulombs and +6microcoulombs are placed 40cm apart. find the loaction along the line joining the two charges when the force on a -2microcoulomb chrage would be zero. consider only locations between the two positive charges

## Homework Equations

E = E1 + E2 = (kqa/r^2) + (kqa/r^2).... where E is electric field, and E1 is electric field of one +charge qa, and E2 is the electric field of the other charge qb

k = 9*10^9 constant

E = F/q where F = force, q is charge = -2microcoulombs, and E is from the first equation

## The Attempt at a Solution

i am not sure if i am using the correct equations

first i used the frst eq and solved for E1 and E2 using the k and the given charges and radius r = 40cm =0.4m, i summed E! and E2 to get E

then used the second equation, and subbed in E from the first eq in for E in the second, used q = -2microcoulombs for q, but the thing is i am trying to find where the force is zero so, if i sub in 0 for F in the second equation i get no where

i need an equation that allows me to factor in force and the q= -2microcoulombs charge. i need to find r

help appreciated..