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).