If , thenSince SinA=4/5 I know CosA=1/5
since A is a quad I or quad II angle,
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)