Answer
$\dfrac{\sqrt{10}}{10}$
Work Step by Step
$\cos{B} =\sqrt{1-\sin^2{B}} = 0.8$
$\sin{\dfrac{B}{2}} = \sqrt{\dfrac{1-\cos{B}}{2}} = \sqrt{\dfrac{1-0.8}{2}}$
$\sin{\dfrac{B}{2}} = \dfrac{\sqrt{10}}{10}$
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