곡면 $z= \sin \left (x y \right)$ 위의 점 $\displaystyle \left (\frac{\pi} {6}, 1, \frac{1} {2} \right)$ 에서의 접평면의 방정식은?

• ①$\displaystyle \frac{1} {2} \left (x- \frac{\pi} {6} \right) + \frac{\pi} {12} \left (y-1 \right) - \left (z- \frac{1} {2} \right) =0$
• ②$\displaystyle \frac{1} {2} \left (x- \frac{\pi} {6} \right) - \frac{\pi} {12} \left (y-1 \right) - \left (z- \frac{1} {2} \right) =0$
• ③$\displaystyle \frac{\sqrt {2}} {2} \left (x- \frac{\pi} {6} \right) + \frac{\sqrt {2} \pi} {12} \left (y-1 \right) - \left (z- \frac{1} {2} \right) =0$
• ④$\displaystyle \frac{\sqrt {3}} {2} \left (x- \frac{\pi} {6} \right) + \frac{\sqrt {3} \pi} {12} \left (y-1 \right) - \left (z- \frac{1} {2} \right) =0$
• ⑤$\displaystyle \frac{\sqrt {3}} {2} \left (x- \frac{\pi} {6} \right) - \frac{\sqrt {3} \pi} {12} \left (y-1 \right) - \left (z- \frac{1} {2} \right) =0$