Download POP Geometric Terms

1. Angle
Two rays sharing a common endpoint. Angles are typically measured in degrees or radians.
Angle
2. Arc of a Circle
A connected section of the circumference of a circle.
Arcs are measured in two ways: as the measure of the central angle, or as the length of the arc itself.
Measurement by
central angle
(degrees)
Measurement by
arc length
(radians)
The red arc (minor arc) measures 120°.
The blue arc (major arc) measures 240°.
Formula: s = rθ
s = arc length
r = radius of the circle
θ = measure of the central angle in radians
Red arc: r = 2 and θ = 2π/3, so s = 4π/3
Blue arc: r = 2 and θ = 4π/3, so s = 8π/3
See also
Arc length of a curve
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB
3. Area of a Circle
The formula is below.
4. Central Angle
An angle in a circle with vertex at the circle's center.
5. Circumference
A complete circular arc. Circumference also means the distance around the the outside of a circle.
6. Chord
A line segment on the interior of a circle. A chord has both endpoints on the circle.
See also
Secant line
7. Perimeter
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB
The distance around the outside of a plane figure. For a polygon, the perimeter is the sum of the lengths
of the sides.
8. Pi π
The ratio of the circumference of a circle to its diameter. Pi is written π and is a transcendental number.
π ≈ 3.14159 26535 89793...
9. Polygon
A closed plane figure for which all sides are line segments. The name of a polygon describes the number
of sides. A polygon which has all sides mutually congruent and all angles mutually congruent is called a
regular polygon.
Number of
sides
Polygon name
3
triangle
4
quadrilateral
5
pentagon
6
hexagon
7
heptagon
8
octagon
9
nonagon
10
decagon
11
undecagon
12
dodecagon
n
n-gon
pentagon
regular undecagon
octagon
10. Radius of a Circle or Sphere
A line segment between the center and a point on the circle or sphere. The word radius also refers to the
length of this segment.
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB
11. Ratio
The result of dividing one number or expression by another. Sometimes a ratio is written as a
proportion, such as 3:2 (three to two). More often, though, ratios are simplified according to the standard
rules for simplifying fractions or rational expressions.
Note: The word "rational" indicates that a ratio (in the second sense) is involved. The word rate also
indicates a ratio is involved, as in instantaneous rate of change or average rate of change.
12. Secant Line
A line which passes through at least two points of a curve. Note: If the two points are close together, the
secant line is nearly the same as a tangent line.
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB
13. Tangent Line
A line that touches a curve at a point without crossing over. Formally, it is a line which intersects a
differentiable curve at a point where the slope of the curve equals the slope of the line.
Note: A line tangent to a circle is perpendicular to the radius to the point of tangency.
.
Point of Tangency
Tangent Line to a Curve
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB
Additional terms if needed:
1. Arm of an Angle
Side of an Angle
Either of the two rays making up an angle.
2. Circle
The locus of all points that are a fixed distance from a given point.
3. Initial Side of an Angle
The ray where measurement of an angle starts.
Angle, terminal side of an angle, side of a polygon
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB
4. Line Segment
Segment
All points between two given points (including the given points themselves).
Example:
line segment
5. Terminal Side of an Angle
The ray where measurement of an angle stops.
See also
Initial side, coterminal angles, side of a polygon
SUSME – Workshop Terms for Melissa
January 22, 2011
UAB