Question

Please help I don't Understand!

Answer 1

Answer: SAS similarity theorem

Proportional relationship:

$\sf \dfrac{AB}{AC} = \dfrac{AM}{AN}$

insert values

$\rightarrow \sf \dfrac{21+9}{14+6} = \dfrac{21}{14}$

simplify

$\rightarrow \sf 1 = 1$

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).