રેખાઓ $\vec{r}=(2 \hat{i}-3 \hat{j}+\hat{k})+\lambda(\hat{i}+4 \hat{j}+3 \hat{k})$ અને $\vec{r}=(\hat{i}-\hat{j}+2 \hat{k})+\mu(\hat{i}+2 \hat{j}-3 \hat{k})$ વચ્ચેનો ખૂણો શોધો.

• A
  $\frac{\pi}{2}$
• B
  $\cos ^{-1}\left(\frac{9}{\sqrt{91}}\right)$
• C
  $\cos ^{-1}\left(\frac{7}{\sqrt{84}}\right)$
• D
  $\frac{\pi}{3}$