Heights and distances problems apply trigonometry to real-world geometric scenarios. The angle of elevation is the angle above the horizontal when looking up at an object; the angle of depression is the angle below the horizontal when looking down. By the alternate interior angle theorem, the angle of depression from A to B equals the angle of elevation from B to A. The primary technique is forming right triangles: in a right triangle, tan(angle) = $\frac{opposite}{adjacent}$ is the most used ratio (relating height to horizontal distance). For problems involving two observation points on level ground at known distance apart, set up two equations using tan of each elevation angle and solve simultaneously. Non-level ground problems require additional angle adjustments.