Pythagoras’ Theorem

In a right-angled triangle, the square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the other two sides: $c^2 = a^2 + b^2$.

Depression refers to the angle below the horizontal line when looking down at an object.

Use the inverse tangent function: $\theta = \tan^{-1}\left(\frac{\text{opposite}}{\text{adjacent}}\right)$.