THE SUM OF THE THREE ANGLES IN a TRIANGLE
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THE SUM
OF THE
THREE
ANGLES IN
A TRIANGLE
GRE
EN
REVISION
Q1.
Line
xy
passes
through
point A and is
parallel to BC.
What is the measure of
angle BAC?
A.
B.
C.
D.
REVISION
Q2.
Line
xy
passes
through
point A and is
parallel to BC.
What
is
the
measure of angle
ABC?
A.
B.
C.
D.
REVISION
Q3.
Line
xy
passes
through
point A and is
parallel to BC.
What
is
the
measure of angle
ACB?
A.
B.
C.
D.
01
THE SUM OF
THE THREE
ANGLES IN A
TRIANGLE
01.THE SUM OF THE THREE ANGLES IN A
TRIANGLE
? Draw a triangle, using a protractor to measure the
1 three angles in this triangle, calculate the sum?
A
C
B
The protractor
01.THE SUM OF THE THREE ANGLES IN A
?2
TRIANGLE
Step 1: Cut a
triangle and label
angles.
Step 2: Cut off
the angle b and
c.
Step
3:
Place
angle b and c
adjacent to the
angle a.
18
0
o
01.THE SUM OF THE THREE ANGLES IN A
TRIANGLE
A
C
B
The sum of three angles of a
triangle is
18
0
o
01.THE SUM OF THE THREE ANGLES IN A
TRIANGLE
Ay
x
1
Proof: Through A, draw
line xy parallel to BC
2
xy // BC (two alternate (1)
interior angles)
B
Given
Prove
C
ABC
xy // BC
(2)
From (1) and (2), we can
conclude that:
Practice
Q1. Given triangle
ABC
with
,.
Compute angle A
In the triangle ABC:
(The sum of three
angles in a triangle
Theorem)
JE SUIS JOLIE
Practice
Q2. Given triangle ABC
with ,
Compute angle A, B.
In the triangle ABC:
(The sum of three
angles in a triangle
Theorem)
Find
two
numbers
when you know the
sum and the ratio
BONJOUR
SALUT
THANK
S
