Question

Sin2x = 2cos^2 x/2 - 1

Answer 1

$sin(2x)=2cos^2(x/2)-1\ 2sinxcosx=2(1+cosx)/2-1\ 2sinxcosx=cosx\ cosx(2sinx-1)=0\ left [[ {{cosx=0} atop {sinx=1/2}} right. \ left [[ {{x= pi /2+ pi n} atop {x=(-1)^n pi /6+ pi n}} right.$