Cambridge O Level Mathematics (Syllabus D) · Syllabus 4024 · Trigonometry
Pythagoras and Trigonometry in 3D
What is Pythagoras and Trigonometry in 3D?
The technique of solving a three-dimensional problem by reducing it to a sequence of flat right-angled triangles, each lying wholly in one plane. A length such as the space diagonal of a cuboid is found in stages: Pythagoras on the base gives the base diagonal, and Pythagoras on the vertical triangle formed by that diagonal and the height gives the space diagonal. The angle between a line and a plane is defined as the angle between the line and its perpendicular projection onto that plane, so the projection must be identified and marked before any ratio is used. No two-dimensional formula may be applied to three lengths that do not lie in a single plane.
This definition is part of the Trigonometry chapter in Cambridge O Level Mathematics (Syllabus D).