My mind is not working to day if SinA=4/5, find sin 1/2A.

So in the formula I need Cos, Since SinA=4/5 I know CosA=1/5 and that is the number I will use in my problem

SO Sin1/2A=Sqrt( (1-Cos(1/5))/2) right?

and if Cosx =-1/2 find sin x/2

I will say SinA=Sqrt((1--1/2)/2)