If θ₁ and θ₂ be the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip θ is given by:

Note that tanθ = V/H.. (1)
where θ is the true value of dip. Here we assumed θ = λ
Now, angles of dips, θ₁ and θ₂ have different formulae
tanθ₁ = V/H × cosλ.. (2)
tanθ₂ = V/H × sinλ.. (3)
From eqn (1), (2), (3), we can find the value of H/V which is cotθ, which when calculated comes to option B
cot²θ₁ + cot²θ₂ = H²/V²(cos²λ + sin²λ) = cot²θ
cot²θ = cot²θ₁ + cot²θ₂