Transcript Angle and Angles Measurement

Two-Dimensional Figures
Geometry
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Warm Up
Classify the angle as acute; right angle, obtuse or straight.
1)
Acute
2)
Right angle
3) Obtuse
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4) Straight
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Polygon
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Flat figures such as squares, rectangles are
two-dimensional figures.
A polygon is a simple, closed, twodimensional figure formed by three or more
sides.
The number of sides determine a polygon’s
name.
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Polygon
Triangle
(3 sides)
Hexagon
(6 sides)
Quadrilateral
(4 sides)
Heptagon
(7 sides)
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Pentagon
(5 sides)
Octagon
(8 sides)
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Polygon
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Tri: three
Quad: four
Penta: five
Hexa: six
Hepta: seven
Octa: eight
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Polygon
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Lateral: comes from the Latin word meaning
side
-gon: comes from the Greek word for angle
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Regular Polygon
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When all sides of a polygon are congruent
and all of the angles are congruent, the
polygon is a regular polygon
The polygon has 5 sides.
So, it is a pentagon. Since
the sides and angles are
congruent, it is a regular
polygon.
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Your Turn!
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Identify the polygon. Then tell if it is a regular
polygon.
The polygon has 7 sides.
So, it is a heptagon.
Since the sides and
angles are not congruent,
it is not a regular polygon.
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Triangles
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Step 1: Draw a triangle similar to the one
shown below. Then tear off each corner.
Step 2: Rearrange the torn pieces as shown.
1
1
2
3
2
3
When you arrange
the angles, a line
is formed.
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By extending the
line, you find 180°
on the protractor.
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Triangles
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Step 3: Repeat Steps 1 and 2 with a different
triangle.
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Therefore, the sum of the measures of the angles
of a triangle.
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Triangles
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Triangles can be classified according to their
angles.
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Acute
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Right
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Obtuse
All angles are acute
One angle is right angle
One angle is obtuse
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Your Turn!
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Find the missing angle measure for each
triangle. Then classify each triangle as acute,
right, or obtuse.
30°
x°
45°
x°
95°
40°
Obtuse
x°
20°
130°
Obtuse
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60°
63°
57°
Acute
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Special names of triangles
Figure
Characteristic
Scalene Triangle
Isosceles triangle
No sides congruent
At least two sides are congruent
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Special names of triangles
Figure
Characteristic
Equilateral triangle
All sides are congruent
All angles are congruent
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Quadrilaterals
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Quadrilaterals can be classified by their sides
and angles.
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Special names of quadrilaterals
Figure
Characteristic
Rectangle
Square
Opposite sides congruent
All angles are at right angles
Opposite sides are parallel
All sides are congruent
All angles are right angles
Opposite sides are parallel
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Special names of quadrilaterals
Figure
Characteristic
Parallelogram
Rhombus
Opposite sides congruent
Opposite sides parallel
Opposite angles congruent
All sides congruent
Opposite sides parallel
Opposite angles congruent
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Your Turn!
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How are rectangles and squares alike? How
do they differ?
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Sample answer: similarities- four sides, closed
figures, opposite sides equal, opposite sides
parallel; differences-squares have four congruent
sides
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Let us take a Break!
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Assessment
Draw an example of each polygon listed.
Mark any congruent sides, congruent
angles, and right angles.
1.
a)
b)
c)
d)
e)
f)
Hexagon
Regular octagon
Parallelogram
Triangle
Equilateral Triangle
Rectangle
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Check student’s responses
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Assessment
Tell whether each statement is sometimes,
always, or never true.
2.
a)
b)
c)
d)
Parallelograms are squares sometimes
A rhombus is a square sometimes
A rectangle is a parallelogram always
A square is a rhombus always
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Review
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A polygon is a simple, closed, twodimensional figure with three or more sides.
When all the sides and angles of a polygon
are congruent, then the polygon is congruent.
Scalene, Isosceles and Equilateral are three
types of triangles
Rectangle, square, parallelogram, and
rhombus are types of quadrilaterals
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Thank You!
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Remember to do the practice worksheets!!!
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