Download Write an equation for the exterior angle of the triangle.

1. ACUTE TRIANGLE - a traingle with three acute
angles.
2. RIGHT TRIANGLE - a triangle with a right angle. ( 90o
angle)
3. OBTUSE TRIANGLE - a triangle with an obtuse
angle.
4. SCALENE TRIANGLE - no sides are the same, no
angles are the same.
5. ISOSCELES TRIANGLE - two sides are the same,
base angles are the same.
6. EQUILATERAL TRIANGLE - all sides are the same,
all angles are the same. ( 60o )
The sum of the angles in a triangle is 180o.
PROOF: Using Parallel Lines.
1 =  4 and  3 =  5
But  1 +  2 +  3 = 180o
If  1 is replaced with  4
and  3 with  5,
then  4 +  2 +  5 = 180o
(Z pattern)
(straight angle)
An exterior (or external) angle is the angle between
one side of a triangle and the extension of an adjacent
side
External angle
PROPERTIES:
An exterior angle of a triangle is equal to the sum of the
opposite interior angles.
In the figure below the exterior angle 1 is equal to the sum
of the angles 3 and 4
External angle
1=3+4
Write an equation for the exterior angle
of the triangle.
Write an equation for the exterior angle
of the triangle.
Exterior angle xo = zo + wo
Calculate the measures of the
unknown angles. State how you know.
Calculate the measures of the
unknown angles. State how you know.
1.  u
= 60o ( supplement to 120o )
2.  t = 30o ( sum of triangle )
3.  s = 60o ( sum of triangle )
4.  r = 120o ( supplement to so )
Class work
 Check
solutions to Lesson 16(2)
 Copy down notes and examples from this
lessson.
 Do Lesson 16(3) worksheet