The quartic formula gives the solutions of `a``x`^{4} + `b``x`^{3} + `c``x`^{2} + `d``x` + `e` = 0 for real numbers `a`, `b`, `c`, `d`, `e` with `a` ≠ 0.

*Directions: Choose all possibilities for the three ± signs with the last two equivalent. Use real cube roots if possible, and principal roots otherwise.*