Published by admin on September 15, 2020 ##theta=(2n+1)pi/2## or ##theta=2npi+-(2pi)/3## where ##n## is an integer. ##cos2theta=costheta## or ##2cos^2theta-1=costheta## (using formula for ##cos2theta##) the above becomes ##2cos^2theta-costheta-1=0## Now using quadratic formula ##costheta=(-(-1)+-sqrt((-1)^2-4*2*(-1)))/(2*2)## or ##costheta=(1+-sqrt(1+8))/4=(1+-3)/4## […]