Step by step
The question
Question: which rule shows that triangles ABC and DEF are congruent?
1 Match the parts
Congruent means the same shape and the same size.
One fits exactly on top of the other.
The order of the letters shows which corners match: A with D, B with E, C with F.
DEF is turned over.
That does not matter.
Angle B and angle E are both 40°: a pair of equal angles.
A for angle.
AC and DF are both 9: a pair of equal sides.
S for side.
AB and DE are both 12: a pair of equal sides.
S for side.
2 Find the rule
Angle B is not between the two sides: AC does not touch corner B.
Go round: side, side, angle: S S A.
Careful: S S A is not a rule.
Look: these two triangles have the same marked parts, but they are different.
So we cannot tell if they are congruent.
There is no answer from these facts.
Let's look back.
First: match the parts.
Last: find the rule.