If cos B = 3/5, then what is the positive value of cos 1/2 B, in simplest radical form with a rational denominator?

cos (B/2) = 2√5 / 5

Step-by-step explanation:

Use half angle formula:

cos² (B/2) = (1 + cos B) / 2

cos² (B/2) = (1 + 3/5) / 2

cos² (B/2) = (8/5) / 2

cos² (B/2) = 4/5

cos (B/2) = 2/√5

cos (B/2) = 2√5 / 5