Triangles ABC and DEF: AB = DE = 5, BC = EF = 7, AC = DF = 6

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.

AB and DE are both 5: a pair of equal sides.

S for side.

BC and EF are both 7: a pair of equal sides.

S for side.

AC and DF are both 6: a pair of equal sides.

S for side.

2 Find the rule

All three pairs are sides.

Side, side, side: S S S.

Three sides fix the triangle.

Like three sticks: they join up in only one way.

So S S S shows the triangles are congruent.

Let's look back.

First: match the parts.

Last: find the rule.