Find work done in rotating an electric dipole of . . .

Question : Find work done in rotating an electric dipole of electric dipole moment 3p in an electric field of intensity E/2 from 

i) stable configuration to unstable configuration

ii) 30° to 120°

Doubt by Mansi 

Solution : 

Electric Dipole Moment = 3p
Intensity of Electric Field = E/2

We know, work done in rotating an electric dipole placed in an Uniform Electric Field from initial angle θ₁ to final angle θ₂ is given by 

W  = pE(cosθ₁-cosθ₂)

i) 
For position of stable equilibrium, θ₁=0°
For position of unstable equilibrium, θ₂=180°

W = (3p)(E/2) [cos0°-cos180°]
W = [3pE/2] [1-(-1)]
W = [3pE/2] [ 1+1]
W  =[3pE/2][2]
W = 3pE

ii) θ1=30° to θ2=120°

W = (3p)(E/2) [cos30°- cos120°]
W = [3pE/2] [(√3/2) - (-1/2)]
W = [3pE/2][(√3/2) + (1/2)]

W = [3pE/2][(√3+1)/2]
W = [3pE(√3+1)]/4