If cosB=1/9, then what is the positive value of cos1/2B, in simplest radical form with a rational denominator?

Question

If cosB=1/9, then what is the positive value of cos1/2B, in simplest radical form with a rational denominator?

Answer 1

cosB=(1/9)

cos(B/2)=√([1+cosB]/2)

            =√([1+(1/9)]/2)

            =√([10/9]/2)

            =√(10/18)

            =√(5/9)

            =√5/√9

            =√5/3