If $\theta_1$ and $\theta_2$ be the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip $\theta$ is given by :

Question

( A ) $\cot^2 \theta = \tan^2 \theta_1 - \tan^2 \theta_2$
( B ) $\cot^2 \theta = \cot^2 \theta_1 - \cot^2 \theta_2$
( C ) $\cot^2 \theta = \tan^2 \theta_1 + \tan^2 \theta_2$
( D ) $\cot^2 \theta = \cot^2 \theta_1 + \cot^2 \theta_2$