જો $\vec{a}=2 \hat{i}+\hat{j}-\hat{k}$, $\vec{b}=\hat{i}-\hat{j}+3 \hat{k}$, $\vec{x}=\left(\frac{\vec{a} \cdot \vec{b}}{|\vec{b}|^2}\right) \vec{b}$, $\vec{y}=\left(\frac{\vec{a} \cdot \vec{b}}{|\vec{a}|^2}\right) \vec{a}$ અને $\theta$ એ $\vec{a}$ અને $\vec{b}$ વચ્ચેનો ખૂણો હોય, તો $x^2+y^2=$

• A
  $17 \cos ^2 \theta$
• B
  $(\sqrt{6}+\sqrt{11}) \cos ^2 \theta$
• C
  $17 \cos 2 \theta$
• D
  $17 \sin ^2 \theta$