MCQ
If $\phi_1$ and $\phi_2$ be the angles of dip observed in two vertical planes at right angles to each other and $\phi$ be the true angle of dip, then
- A(a) $\cos ^2 \phi=\cos ^2 \phi_1+\cos ^2 \phi_2$
- B(b) $\sec ^2 \phi=\sec ^2 \phi_1+\sec ^2 \phi_2$
- C(c) $\tan ^2 \phi=\tan ^2 \phi_1+\tan ^2 \phi_2$
- D(d) $\cot ^2 \phi=\cot ^2 \phi_1+\cot ^2 \phi_2$
