When I first started out in digital photography I was initially lead astray by all the misinformation on the www and elsewhere the Exposure Triangle (ET) supposedly teaches.
The ET taught me that to maintain a constant exposure after changing one of aperture, shutter speed or ISO I needed to adjust one of the other two parameters by the reciprocal amount.
For example, the ET taught that for a given scene and lighting:
A. f/8, 1/400s, ISO 200
and
B. f/8, 1/200s, ISO 100
were the same exposure because both settings output the same image lightness.
After finally realising and accepting, by listening to people who actually knew what they were talking about, that exposure is the amount of light striking the sensor per unit area while the shutter is open I saw that the ET and its teachings is totally inconsistent with the established technical definition of exposure*.
Although both settings A and B will output the same image lightness, setting A will have had only half the exposure* of setting B and so the image from setting A will have more visible noise in the shadows because of the lower Signal to Noise Ratio due to the smaller exposure*.
At best, with the ET you could say that for a constant image lightness, not exposure*, there is an inverse relationship between any two of aperture, shutter speed and ISO. You shouldn't need a triangle or any other shape to understand that simple and basic concept, so the ET is unnecessary.
* exposure - amount of light striking the sensor per unit area while the shutter is open
** optimal exposure - the maximum exposure* within dof and motion blur requirements without clipping important highlights.
*** under exposed - more exposure* could have been added with the DOF and blur constraints still being met without clipping important highlights.