Download 4.1: Congruent Figures

Bell Work:
1.
Identify the angle relationships in the figure
to the right
2.
Are any of the lines parallel? How do you
know?
3.
Write the equation of a line in slopeintercept from which has a slope of 7 and a
y-intercept of -3
4.1: Congruent
Figures
Notes

For two figures to be congruent, every part of each
figure must be congruent. All angles and lines must
correspond exactly with one angle or line on the other
figure.

Theorem 4-1: Third Angles Theorem
If two angles of one triangle are congruent to two
angles of another triangle, then the third angles must be
congruent as well.

Assume these triangles are congruent…

What is the measure of angle D?

What can we conclude about the side
lengths of the triangles?

If we changed the scale of the jet on the
right, what would happen to the side
lengths of the triangles?

If we changed the scale as in the question
above, would the triangles still be
congruent?
 Are
these figures
congruent?
Justify your
answer.
Congruent Triangles

How many conditions
must be found to show
two triangles are
congruent?

How do we know the
third sides are
congruent?

How do we know the
third angles are
congruent?

What do we need in order for these two
triangles to be congruent?

What do they have in common?
Are these triangles congruent?
4.2: Congruent
Triangles using SSS
and SAS
What can we
conclude
about the two
triangles?

Postulate 4-1: Side-Side-Side (SSS) Postulate
If all three sides of two triangles are congruent to
each other, then the triangles are congruent
Can we
conclude these
triangles are
congruent?

Postulate 4-2: Side-Angle-Side (SAS) Postulate
If two sides and the angle between them of
one triangle are congruent to two sides and the
angle between them of another triangle, the
triangles are congruent
Using SAS
Homework:
4.1,
page 222: 22, 23, 24, 30,
40
Honors: Add 34, 44
4.2, page 231: 11-14, 16, 18
Honors: Add 22, 26