Video narration
How can you find the height of a wall without climbing it? Lean a ladder against it, and the wall, ground, and ladder form a right triangle. Choose the angle where the ladder meets the ground. The ladder is the hypotenuse: the longest side, opposite the right angle. The wall is opposite that angle, and the ground is adjacent, next to it. Here's the turn: the angle is not just a corner. It fixes the side-length ratios. Sine is opposite divided by hypotenuse; cosine is adjacent divided by hypotenuse; tangent is opposite divided by adjacent. Measure the ladder's angle and one suitable side; choose the ratio connecting them to the unknown side. These ratios work for right triangles, and opposite and adjacent depend on which angle you choose. So measure the ladder's angle and a side; sine, cosine, or tangent reveals the wall's height.