You can know if a triangle is similar if they're congruent or have 2 of the same length and same angle SAS, if they have the same lengths SSS, if the have 2 of the same angles and 1 same length ASA or AAS.
The answer to this question is A prime number. A prime number has only two factors one an itself. Opposite to composite which has more than two. Example! Prime:2,3,5,7 Composite:4,6,8,9
