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 

(1) $co{t}^2\theta =co{t}^2{\theta }_1+co{t}^2{\theta }_2$

(2) ${\tan }^2\theta ={\tan }^2{\theta }_1+ {\tan }^2{\theta }_2$

(3) $co{t}^2\theta =co{t}^2{\theta }_1-{\tan }^2{\theta }_2$

(4) ${\tan }^2\theta ={\tan }^2{\theta }_1-{\tan }^2{\theta }_2$

If ${\theta }_1$ and ${\theta }_2$ are 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:
1. ${\tan }^2\theta ={\tan }^2{\theta }_1+ta{n}^2{\theta }_2$
2. $co{t}^2\theta =co{t}^2{\theta }_1-co{t}^2{\theta }_2$
3. ${\tan }^2\theta ={\tan }^2{\theta }_1+ta{n}^2{\theta }_2$
4. $co{t}^2\theta =co{t}^2{\theta }_1+co{t}^2{\theta }_2$