The fundamental equation of trigonometry states that
[tex] \cos^2(x)+\sin^2(x)=1 [/tex].
This derives from the fact that any point on the unit circle has coordinates [tex] (x,y) = (\cos(x),\sin(x)) [/tex], together with the fact that the equation of the unit circle is [tex] x^2+y^2=1 [/tex]
So, from the fundamental equation you can deduce
[tex] \sin^2(x) = 1-\cos^2(x) [/tex]
which in your case leads to
[tex] \sin^2(x) = 1-0.36 = 0.64 [/tex]
