일반물리학 2 — Coulomb's Law: Problem 10

10 Figure 21-13 shows electrons 1 and 2 on an $x$ axis and charged ions 3 and 4 of identical charge $-q$ and at identical angles $\theta$. Electron 2 is free to move; the other three particles are fixed in place at horizontal distances $R$ from electron 2 and are intended to hold electron 2 in place. For physically possible values of $q \le 5e$, what are the (a) largest, (b) second largest, and (c) third largest values of $\theta$ for which electron 2 is held in place?