Download 1.5 Triangle Vocabulary

Homework:
1.5/1-14, 17-21, 24-26
Quiz Friday on Lesson 1.3 – 1.5
To assume something is to accept it as
true without facts or proof.
 When looking at a diagram, be careful
not to assume anything

 Lines
are straight
 If two lines intersect, they intersect
at one point
 Points on a line are collinear
 All points shown in a diagram are
coplanar unless additional planes
are shown
Just because they look:
 parallel
› two lines or segments are NOT
necessarily parallel
 perpendicular
› two lines are NOT necessarily
perpendicular
 Congruent
› pairs of angles, segments, or polygons
are NOT necessarily congruent
All CONGRUENT,
PARALLEL,
PERPENDICULAR
parts MUST be
MARKED
A
triangle has three sides and three angles
 The three angles always add to 180°
 There are special names given to triangles
that tell how many sides or angles are
equal.
 There can be 3, 2 or no equal sides/angles:
› Sides: Equilateral, Isosceles and Scalene
› Angles: Acute, Right, Obtuse, and Equiangular
Equilateral Triangle
Three equal sides
Isosceles Triangle
Two equal sides
Scalene Triangle
No equal sides
Acute Triangle
All angles are between 0°and 90°
Right Triangle
Has exactly one right angle (=90°)
Obtuse Triangle
Has one angle between 90° and 18
Equiangular Triangle
Three equal angles, always 60°
Sometimes a triangle will have two
descriptive names.
 One for angles & one for sides
For example:
 Right Isosceles Triangle

› It has a right angle (90°), and also two equal
angles

Can you guess what the measure of the
equal angles are?
 YES
Scalene right triangle?
 NO
 Obtuse acute triangle?
 Equiangular scalene triangle?  NO
 YES
 Isosceles right triangle?
 NO
 Equilateral obtuse triangle?

 Sketch
› To create the picture with only a pencil;
freehand
 Draw
› To use measuring tools: ruler and protractor
 Construct
› To use construction tools: compass and
straightedge
These terms will determine what
tools, if any, you are
required/allowed to use.
1.
2.
M
1.
N
A
2.
O
P
Y
U
3.

4.

ΔBAD with BA = 2.5 cm, m<A = 75˚
Right scalene ΔHOP with right angle P,
PO = 4cm, PH = 2cm.
D
3.
B
4.
75˚
2.5cm
A
H
2cm
P
4cm
O