Which of the following is a third root of the given complex number.

Answer:4(cos(15π/21) +i·sin(15π/21))4(cos(π/21) +i·sin(π/21))Step-by-step explanation:The third root of the number 64∠(π/7) will be ...   64^(1/3) ∠((π/7 +2nπ)/3) . . . . for n = 0, 1, 2 (angles repeat after that)   = 4 ∠((π/21)(1+14n)) . . . . . . . . for n = 0, 1, 2   = 4∠(π/21), 4∠(15π/21), 4∠(29π/21)Of these three third roots, only the first two are listed among the answer choices. In your preferred form, they are ...4(cos(π/21) +i·sin(π/21)) . . . . . . . . . matches 3rd choice4(cos(15π/21) +i·sin(15π/21)) . . . . . matches 1st choice