To find the coordinates of point B we need to notice that this points is on the quarter of a circle shown in the picture. This circle have radius one.
Now, from the definitions of the sine ans cosine function we conclude that for point B(x,y):
[tex]\begin{gathered} x=\sin 45=\frac{\sqrt[]{2}}{2} \\ y=\cos 45=\frac{\sqrt[]{2}}{2} \end{gathered}[/tex]Therefore the coordinates of the point B are:
[tex]B(\frac{\sqrt[]{2}}{2},\frac{\sqrt[]{2}}{2})[/tex]