Q.The equation of the plane containing the lines $\vec{r} = \hat{i} + \hat{j} - \hat{k} + \lambda (2\hat{i} + \hat{j} - \hat{k})$ and $\vec{r} = \hat{i} + \hat{j} - \hat{k} + \mu (\hat{i} + 2\hat{j} - \hat{k})$ is