Geometry Flashcards
Collinear
Three or more points on same line
Line
Defined by two distinct points and contains an infinite number of points
Segment
A line bounded at both ends
Segment Bisector
A line that goes through the midpoint of a segment, dividing the segment into two equal parts
Perpendicular AKA
AKA Orthogonal
Perpendicular lines
Meet at 90* right angles
Perpendicular line slopes
Negative reciprocals
Parallel line slopes
Identical slopes
Distance Formula
√ (x2-x1) ^2+ (y2-y1)^2
Slope
(x2-x1) / (y2-y1)
Midpoint (between two points)
[(x1+x2)/2 , (y1+y2)/2]
Angle
The intersection of two non-identical lines
Angle Bisector
A line through the vertex that divides the angle into two equal angles (point is equidistant from sides).
Vertex
The point of intersection
Coplanar Angles
Lie in the same plane but are not necessarily adjacent
Adjacent Angles
Share a common side
Vertical Angles are…
Congruent (Angles opposite each other where two lines cross)
Acute angle
Less than 90*
Right angle
Equals 90*
Obtuse angle
Greater than 90*
Linear pair
Two angles that form a straight angle
Congruent figures
Same shape and same size
Congruent Triangles proofs
Side-Angle-Side, Side-Side-Side, Angle-Side-Angle, or Angle-Angle-Side
Similar figures
Congruent angles and proportional sides
Relation
Mapping of input values to output values, or x to y
Reflexive relation
Can map x to itself (ie: x=x)
Symmetric relation
If a=b, then b=a
Transitive relation
a=b, b=c, therefore a=c
Equivalence Relation
Is reflexive, symmetric and transitive
Irregular/Scalene Triangle
Has NO sides that are the same length and NO angles that are the same measure
Scalene Triangle AKA
AKA Irregular Triangle
Isosceles Triangle
2 sides that are the same length and 2 angles that are the same measure
Equilateral Triangle
All 3 sides of equal length and all 3 angles of equal measure
If a² + b² = c²
Triangle is right
If c² (longest side) is more than a² + b²
Triangle is obtuse
If c² (longest side) is less than a² + b²
Triangle is acute
Area (of a triangle)
(1/2) base x height
Perimeter (of a triangle)
Sum of Sides
Longest side (of a triangle) is opposite which angle?
Largest Angle
Shortest side (of a triangle) is opposite which angle?
Smallest Angle
Median of a triangle
Bisects a side and passes through opposite vertex

Perpendicular Bisector of a triangle
Splits side, right angle to side

The Exterior Angle of a triangle equals…
The sum of the two remote interior angles
Side of a triangle must be less than…
The sum of the other two sides
Side of a triangle must be more than…
The difference of the other two sides
For 45-45-90 triangles, the hypotenuse is…

For 30-60-90 triangles, the length of the longer leg is ___ times the length of the shorter leg
√3

For 30-60-90 triangles, the hypotenuse is ___ the length of the shorter leg
2x

Sine = (Ratio only true for right angles)
opposite/hypotenuse
Cosine = (Ratio only true for right angles)
adjacent/hypotenuse
Tangent = (Ratio only true for right angles)
opposite/adjacent
Cosecant = (Ratio only true for right angles)
1/sine
Secant= (Ratio only true for right angles)
1/cosine
Cotangent = (Ratio only true for right angles)
1/tangent
Law of Cosines
a² = b² + c² - 2bc cosA
Ray
A line that begins at an initial point and extends infinitely in one direction
Altitude
A segment perpendicular to a side that goes through the opposite vertex (all meet at a point which might be outside the triangle)
Triangle midline
- A line segment from midpoint of one side to midpoint of another
- Length equals half the third side
- Midline parallel to third side
Geometric mean between a and b
x^2 = ab (ie: geometric mean between 4 and 9 = 6).
Radius (of a circle)
Distance from center to the circle
Diameter (of a circle)
2r distance between opposite points on the circle
Area (of a circle)
πr^2
Circumference (of a circle)
2πr or πd
Arc (of a circle)
a portion of the circumference
Minor Arc (of a circle)
less than 180*
Major Arc (of a circle)
greater than 180*
Chord (of a circle)
a segment with both ends on the circle
Secant (of a circle)
containss a chord and extends beyond the circle
Tangent (of a circle)
touches a circle at single point
Central Angle (of a circle)
An angle formed by two radii with the vertex at the center of the circle. This measure equals the arc it defines.
Measure of an Inscribed Angle (of a circle) is equal to…
1/2 the measure of the intercepted arc
Circumscribed figures (of a circle) are located on the…
outside
Inscribed figures (of a circle) are located on the…
inside
Area of a Sector is proportional to the…
central angle
A (sector)
pi r^2 (theta/360)
Quadrilateral
4 sided, sum of interior angles = 360
Parallelogram
A quadrilateral with 2 sets of parallel sides
Rectangle
A quadrilateral [and special type of parallelogram] with 4 right angles
Square
a rectangle with four equal sides
Rhombus
A quadrilateral with all sides of equal length
A parallelogram with four equal sides but not necessarily with 4 right angles. The diagonals are perpendicular
Trapezoid
has two parallel bases
Regular polygon
has equal sides and equal angles
Sum of interior angles of an n-gon =
180(n-2)
Apothem
The perpendicular bisector of a side that extends to the center of the polygon

Area of a regular polygon =
1/2 (Apothem x Perimeter)
Exterior Angle of a Polygon is created by….
extending one of the sides
The sum of the exterior angle and the adjacent angle of a polygon =
180, a linear pair
The sum of all exterior angles (of a polygon) in the same direction =
360
Midpoint between two points (a,b) and (c,d)
( [a+c]/2, [b+d]/2) think of the avg of the x coords, and avg of y coords
Distance between two points (a,b) and (c,d)
sq rt [(a-c)^2 + (b-d)^2]
Area of a trapezoid
1/2 (b1+b2) (h)
Complementary Angles
Two angles that add up to 90*
Supplementary
Two angles that ad up to 180
If A=C in equation: Ax^2+Bx+Cy^2+Dy+E
circle
If A≠C, but same sign in equation: Ax^2+Bx+Cy^2+Dy+E
ellipse
If A=0 or C=0 in the equation: Ax^2+Bx+Cy^2+Dy+E
parabola
If A and C are opposite sign in the equation: Ax^2+Bx+Cy^2+Dy+E
hyperbola
directrix
a line in the plane
eccentricity
a measure of the shape. the closer to zero, the closer the shape is to a circle.
two parallel lines, two intersecting lines, or three points define a….
plane
two lines that are not parallel and do not meet are…
skew
A line that is perpendicular to a plane is perpendicular to all lines in the plane that passes through the point of…
intersection
A line that intersects a plane must be perpendicular to at least ___ line in the plane
one
Prism
has two congruent, parallel bases (a triangular prism has two parallel triangle bases, a rectangular prism has 2 rectangular bases, etc)
Volume of a Prism
BH (base area * height)
Surface Area of a Prism
2xBase Area + Lateral Area
Volume of a Cylinder
πr^2 x h

Surface Area of a Cylinder
2 π r h + 2 π r^2
Volume of a Cone

Surface Area of a Cone

Slant Height of a Cone
apply pythagorean theorem
square root of altitude^2 + radius^2

Volume of a Pyramid
1/3 x Base area x Height
Surface Area of a Pyramid
B + (Perimeter x slant) / (2)
Volume of a Sphere

Surface Area of a Sphere

Cross Section
Made by slicing through a 3D object to produce a 2D polygon
The cross section of a sphere is a…
circle
The cross section of a triangular prism is a…
triangle or rectangle
The cross section of a pyramid with a square base is a…
square or triangle
Transformation
changes the position of a shape on a coordinate plane — shape is moving from one place to another
Flip/Reflection
A shape is transposed across a line and faces the opposite direction
Slide/Translation
An entire shape moves in a straight path. All points on the shape move an equal distance in the exact same direction
Turn/Rotation
A shape moves in a circular path around an axis point
Isometry
Transformation in two or three dimensions that preserves distance, shape and size
Dilation
Transformation that retains shape but changes size. Resulting image is in proportion (or scale) to original
Similar shape
congruent angles and proportional sides
If the side of a square is doubled, the area increases by a factor of…
^2
If the side of a cube is doubled, the volume increases by a factor of…
^3
If the radius of a circle is doubled, the circumference is doubled, and the area increases by a factor of…
^2
pentagon
5 sides
hexagon
6 sides
octagon
8 sides
heptagon
7 sides
nonagon
9 sides
decagon
10 sides
trapezoid
a convex quadrilateral with at least one pair of parallel sides
Centroid (of a circle) how to find…
The point of concurrency for the medians of a triangle (bisecting each line segment). Centroid is the point of balance for any triangle.
Incenter (of a circle) how to find…
The point of concurrency of the angle bisectors
Circumcenter (of a circle) how to find…
The point of concurrency of the perpendicular bisectors
Conversion formulas to convert from polar coordinates to rectangular coordinates.
x = (r)cosθ and y = (r)sinθ
Outside Angles Theorem (tangents or secants of circles)
1/2 (major arc - minor arc) = angle of the outside angle
Distance from a point to a line formula (h, k) and Ax + By + C = 0
|Ah + Bk + C| over SqRt A^2 + B^2
Interior angles of a regular polygon
180(n-2)
Exterior angles of a regular polygon
360/n
Golden ratio
Approx 1.618 : 1
Angle Bisector of a triangle
- Splits an angle and extends to a side
- Meeting point is equidistant from the sides
Altitude of a Triangle
- Segment perpendicular to a side that goes through opposite vertex
- All point meet, which might be outside the triangle