Answer
$\frac{1}{4}(2+\sqrt 2)$
Work Step by Step
$ sin^2\frac{3\pi}{8}=\frac{1}{2}(1-cos\frac{3\pi}{4})=\frac{1}{2}(1+\frac{\sqrt 2}{2})=\frac{1}{4}(2+\sqrt 2)$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.