Find 4 values of following in exponential forms ?

Find 4 values of following in exponential forms ?

(sqrt3 -i)^(1/4)(3i)14

1 Answer
Jan 17, 2018

See below

Explanation:

let
sqrt3-i=x^43i=x4

x^4 = 2(sqrt3/2-i/2)x4=2(32i2)

x^4 = 2[cos(-pi/6) + isin(-pi/6)]x4=2[cos(π6)+isin(π6)]

x^4 = 2[cos(2mpi - pi/6) + isin(2mpi - pi/6)]x4=2[cos(2mππ6)+isin(2mππ6)]

(This small addition will not the change the value of the equation. Check out yourself.)

x = 2^(1/4)[cis(2mpi-pi/6)]^(1/4)x=214[cis(2mππ6)]14

Short form of writing costheta + isintheta = cisthetacosθ+isinθ=cisθ

x=2^(1/4)[cis((2mpi)/4 - (pi/6)*1/4)]x=214[cis(2mπ4(π6)14)] (applying Demoveries theorm)

x = 2^(1/4)[cis((mpi)/2-pi/24)]x=214[cis(mπ2π24)]

Since the equation was of degree 4, there will be only four roots.

1st root
putting m =0

x = 2^(1/4)[cis(-pi/24)] = 2^(1/4)*e^(-ipi/(24))x=214[cis(π24)]=214eiπ24

2nd root
putting m =1

x = 2^(1/4)[cis((11pi)/24)] = 2^(1/4)*e^(i(11pi)/(24))x=214[cis(11π24)]=214ei11π24

3rd root
putting m =2

x = 2^(1/4)[cis((23pi)/24)] = 2^(1/4)*e^(i(23pi)/(24)x=214[cis(23π24)]=214ei23π24

4th root
putting m =3

x = 2^(1/4)[cis((35pi)/24)] = 2^(1/4)*e^(i(35pi)/(24))x=214[cis(35π24)]=214ei35π24