Answer: SAS similarity theorem
Proportional relationship:
[tex]\sf \dfrac{AB}{AC} = \dfrac{AM}{AN}[/tex]
insert values
[tex]\rightarrow \sf \dfrac{21+9}{14+6} = \dfrac{21}{14}[/tex]
simplify
[tex]\rightarrow \sf 1 = 1[/tex]
L.H.S = R.H.S
The triangles are congruent and follows the rule SAS similarity theorem.
The triangles has/starts from the same angle, corner (A).
