How about "figure"?
there shape is the same
They are said to be congruent
Same way you always calculate volume. The material makes no difference the shape is what's important.
calculate the length of each side then add them all up same with any 2d shape
The opposite of congruent is incongruent, meaning not the same size or shape.
Purchase has the same meaning.
That they all have the same shape and sometimes size
The ordinary meaning of "common" is used in math too. It means "same for both" or "same for all".
The term meaning having the same characteristics is two words, "in common"(e.g. they have a lot in common).The term meaning not common, or rare, is "uncommon."
That they all have the same shape and sometimes size
That they all have the same shape and sometimes size
It means the same shape and size, although not orientation.