Let \(f(x)=\frac{\sin x+\cos x-\sqrt{2}}{\sin x-\cos x}, x \in[0, \pi]-\left\{\frac{\pi}{4}\right\}. \) Then \( f\left(\frac{7 \pi}{12}\right) f^{\prime \prime}\left(\frac{7 \pi}{12}\right)\) is equal to
1
\( \frac{-2}{3}\)
2
\( \frac{2}{9}\)
3
\( \frac{-1}{3 \sqrt{3}}\)
4
\( \frac{2}{3 \sqrt{3}} \)