Question

half angle of 3pi/8

Answer 1

have you covered the half-angle identities yet?

Answer 2

yes

Answer 3

site is sorta lagged thus

anyhow so \(\bf 2\cdot \cfrac{3}{8}\implies \cfrac{6}{8}\implies \cfrac{3}{4}\qquad thus
\\ \quad \\
2\cdot \cfrac{3\pi}{8}\implies \cfrac{3\pi}{4}\qquad thus
\\ \quad \\
sin\left(\frac{3\pi}{8}\right)\implies sin\left(\cfrac{{\color{brown}{ \frac{3\pi}{4}}}}{2}\right)=\pm \sqrt{\cfrac{1-cos\left({\color{brown}{ \frac{3\pi}{4}}}\right)}{2}}\)