Geometry Vocabulary
Line A straight path that continues forever in both directions.
Endpoint A point that STOPS a line from continuing forever, it is a point at the end of a line segment or ray.
Ray A part of a line with one endpoint. The other side continues forever.
Line Segment a segment means a piece or part of something a line segment is a part of a line with 2 endpoints
You try! What is the difference between a line, a line segment, and a ray?
A line: has no endpoints A ray: has 1 endpoint A line segment: has 2 endpoints
Types of Lines Some types of lines we will use are 1. Intersecting Lines 2. Parallel Lines 3. Perpendicular Lines
Intersecting Lines intersect means to cross intersecting lines are lines that cross at one point
Parallel Lines Parallel lines are lines that remain the same distance apart over their entire length. No matter how far you extend them they will never meet.
Perpendicular Lines Perpendicular lines are two lines that cross each other at an exact 90 right angle. 90
You try!! What kind of lines are these? Parallel?? Intersecting?? Perpendicular??
Intersecting! Those lines are intersecting lines because they cross, but not at a 90 angle.
Diagonals A diagonal of a polygon is any straight line that connects two sides that are not next to each other.
Angle An angle formed by two rays or two line segments that share an endpoint called a vertex. ANGLE!!!!
Angle Measure A degree is the unit of measure for the size of an angle. The symbol for degrees is, so we write 30 degrees as 30. Degrees can range from 1 to 360.
We can measure angles with a tool called a protractor.
Protractor: a tool to measure angles in degrees
There are 5 different kinds of angles, based on their size... 1. Right Angle 2. Acute Angle 3. Obtuse Angle 4. Straight Angle 5. Reflex Angle (we won t learn about these in 4th grade)
Right Angle A right angle is an angle that measures exactly 90. 90
Acute Angle An angle with a measure less than 90.
You try! Which angle is acute? 100? 60? 175?
60 is acute because it measures less than 90!!
Obtuse Angle An obtuse angle is an angle that measures greater than 90 and less than 180.
Straight Angle A straight angle is an angle that measures exactly 180. This angle looks like a straight line. 180
You try it! Which picture shows an obtuse angle?
Good job! This angle is obtuse because its measure is greater than 90 degrees!
Open Figures An open figure is a figure that begins and ends at different points. examples:
POLYGONS Lines can form all kinds of different shapes. A polygon is defined as a closed figure with three or more straight sides.
Keep in mind... Open and closed figures may have curved lines, BUT Polygons are closed figures with straight sides only!
Classifying Polygons Polygons are classified by the number of sides they have.
These are the names of different polygons.
You try it! What kind of polygon is this?
Pentagon! This shape is a pentagon because it has five sides. 1 2 5 3 4
TRIANGLES Now that we know polygons and angles, we can see how 3 sides and angles come together and form different triangles.
Triangle A tricycle has three wheels. So a triangle is a polygon made up of three sides and three angles!
Important Information When you add all the degree measures in a triangle, the sum of the three angles is always equal to 180. Triangles are classified in two ways: 1. by the measure of their angles, and 2. by the length of their sides, SO all triangles have TWO names!
Using Angle Measure to Classify Triangles All triangles have at least two acute angles. You look at the 3rd angle to classify it. 1. Acute Triangle: has 3 acute (less than 90 ) angles. 2. Right Triangle: has one right (90 ) angle. 3. Obtuse Triangle: has one obtuse (greater than 90 ) angle.
Right Triangle A right triangle is a triangle with ONE right angle. 90
Acute Triangle An acute triangle is a triangle with three acute angles (angles less than 90 ).
Obtuse Triangle An obtuse triangle is a triangle with one angle that measures greater than 90. greater than 90
You try!! What is the difference between the angles of acute, right, and obtuse triangles?
acute has THREE acute angles. a right triangle has ONE right angle and TWO acute angles. an obtuse triangle has ONE angle greater than 90 and TWO acute angles.
Using Length of Sides to Classify Triangles 1. Equilateral Triangle 2. Isosceles Triangle 3. Scalene Triangle
Equilateral Triangle An equilateral triangle is a triangle with three equal sides. (It will always have three 60 angles.)
Isosceles Triangle An isosceles triangle is a triangle where at least TWO side lengths are the same.
and, This is a scalene triangle because it has three unequal side lengths.
Scalene Triangle A scalene triangle describes a triangle whose side lengths are all different so no two sides are the same length.
Your turn! Which picture shows a scalene triangle? Which picture shows an isosceles triangle?
You got it! This is an isosceles triangle because it has TWO side lengths which are the same.
Quadrilaterals A special type of polygon is a quadrilateral. A quadrilateral is a polygon that has exactly four sides. There are many types.
Quadrilaterals A parallelogram is a quadrilateral that has two pairs of opposite, parallel sides.
Quadrilaterals A rhombus is a special type of parallelogram. It has two pairs of parallel sides and all four sides are equal. Note: A rhombus is a parallelogram, but not all parallelograms are a rhombus.
Quadrilaterals A rectangle is a quadrilateral and parallelogram that has four right angles.
Quadrilaterals A square is a quadrilateral, parallelogram, rhombus, and rectangle that has four right angles and four equal sides. Note: a square can be a rectangle also because it has four right angles. However, a rectangle is not a square.
Quadrilaterals A trapezoid is a quadrilateral that has exactly ONE pair of parallel sides.
Quadrilaterals review What type of quadrilateral are these? a. b. c.
Quadrilaterals review a. This is a trapezoid because it has one pair of parallel sides. b. This is a rhombus because it has 2 pairs of parallel sides, and all four sides are equal, but it does NOT have 4 right angles. c. This is a rectangle because it has four right angles and two pair of parallel sides.
A Line of Symmetry is used to determine if 2 parts of a figure are congruent (exactly the same size and shape).
Lines of Symmetry A shape has symmetry when it can be folded in half and the two sides match up perfectly. A shape can have more than one line of symmetry.
Symmetry Polygons can often have more than one line of symmetry.
You try it! Which of these letters has/have line symmetry? A T L
Right! The letters A and T both have line symmetry. A T
Great job reviewing the Geometry Vocabulary. Keep practicing!