If you asking where you'd find them in the real world - Binoculars and telescopes are two examples.
There is no such thing as a "triangular" number (as a number), a triangular number or triangle number counts the objects that can form an equilateral triangle. One object can and Three objects can but not Two objects.
prism
A triangular number or triangle number counts the objects that can form an equilateral triangle. 10 objects can be formed into an equilateral triangle.
honeycomb
roof
Some of the pyramids in Antarctica resemble a triangular pyramid.
Roof of a house
tent
If you asking where you'd find them in the real world - Binoculars and telescopes are two examples.
what is the study of the design, form and function of objects in the real world
There is no such thing as a "triangular" number (as a number), a triangular number or triangle number counts the objects that can form an equilateral triangle. One object can and Three objects can but not Two objects.
Tent.
prism
Toblarone
a tent
nothing