There's a lot of triangular relationships in photography, and maybe I'm just trying to hard to see it.

There's the exposure triangle with aperture, shutter speed, ISO.

There's the triangular shapes in framing/composing the frame that makes the image "interesting" in how it draws the eye.

There's also the Rule of Thirds, but while not a triangle it is still "3" related

the "technique, equipment, essence" threesome got me on this tangent