Question

find sin1/2B, when cosB = 12/13

Answer 1

\[\cos 2B=2\cos ^2B-1=2(\frac{12}{13})^2-1=\frac{119}{169}\]

Answer 2

\[\cos ^22B+\sin ^22B=1=\frac{119}{169}^2+\sin ^22B=1\]

Answer 3

\[\sin ^22B=1-\frac{14161}{28561}=\frac{14400}{28561}\]

Answer 4

\[\sin 2B=\frac{120}{169}\]

Answer 5

\[\frac{1}{\sin 2B}=\frac{169}{120}\]

Answer 6

B=1/(cos(12/13))
=0.39479
therefore, (sin1)/2(1/(cos(12/13)))
=1.0657