Solution:
Given:
[tex]cos\theta=-\frac{\sqrt{2}}{2}[/tex][tex]\begin{gathered} \theta=cos^{-1}(-\frac{\sqrt{2}}{2}) \\ \theta=135^0 \\ \\ In\text{ the third quadrant, } \\ \theta=180+45 \\ \theta=225^0 \end{gathered}[/tex]
Hence,
[tex]sin225^0=-\frac{\sqrt{2}}{2}[/tex]
Therefore, the correct answer is OPTION A.
