Neet 2017

If θ₁ and θ₂ be the apparent angles of dip observedin two vertical planes at right angles to each other,then the true angle of dip θ is given by (1) cot²θ = cot²θ₁ + cot²θ₂ (2) tan²θ = tan²θ₁ + tan²θ₂ (3) cot²θ = cot²θ₁ – cot²θ₂ (4) tan²θ = tan²θ₁ – tan²θ₂

Please explain it in a really easy way.. This question is really hard for me​