http://www.ck12.org Chapter 4. Triangles and Congruence
4.3 Congruent Triangles
Here you’ll learn what it means for two triangles to be congruent, and how to find the corresponding parts of
congruent triangles.
What if you had a quilt whose pattern was geometric and made up of several congruent figures? In order for these
patterns to come together, the quilter rotates and flips each block (in this case, a large triangle, smaller triangle, and
a smaller square) to get new patterns and arrangements.
How many different sets of colored congruent triangles are there? How many triangles are in each set? How do
you know these triangles are congruent? After completing this Concept, you’ll be able to use your knowledge of
congruent triangles in order to answer these questions.
Watch This
MEDIA
Click image to the left for more content.CK-12 Foundation: Chapter4CongruentTrianglesA
MEDIA
Click image to the left for more content.James Sousa:Congruent Triangles
Guidance
Recall that two figures are congruent if and only if they have exactly the same size and shape. If two triangles
are congruent, they will have exactly the same three sides and exactly the same three angles. In other words, two
triangles are congruent if you can turn, flip, and/or slide one so it fits exactly on the other.
4 ABCand 4 DEFare congruent because
AB∼=DE^6 A∼=^6 D
BC∼=EF and^6 B∼=^6 E
AC∼=DF^6 C∼=^6 FNotice that when two triangles are congruent their three pairs of corresponding angles and their three pairs of
corresponding sides are congruent.