Question 871009
sin(2theta)sin(theta) = cos(theta) 

2sin (theta)cos(theta). sin(theta)=cos(theta)

2sin^2(theta)cos(theta)=cos(theta)

2sin^2(theta) =cos(theta)/cos(theta)

2 sin^2(theta) = 1

sin^2(theta)=1/2

sin (theta)= +/- {{{1/sqrt(2))}}}

so you can find theta