Geometry Flashcards
Angles that form a straight line measure…
180 degrees
A transversal forms how many angles ?
8
Describe a transversal
A line that intersects two or more parallel lines
What are the two distinct angles a transversal forms ?
A big angle larger than 90 degrees. And a small angle smaller than 90 degrees
What is the sum rule to remember for transversals ?
The sum of any big angle and small angle formed by a transversal is 180 degrees
What should you always do when working with a problem with a transversal?
Label all 8 angles so that angle relationships are easier to distinguish
What do you call a line that splits an angle or line segment in half
A bisector
What is a midpoint?
Any point that lies in the middle of a line segment
How do you approach a number line problem?
Label the line segments
Set up equations and Rewrite the given information algebraically
Plug the equation into one another
What is a polygon?
A closed figure formes by 3 or more line segments
What do you call the line segments of a polygon?
Sides
What is a point of intersection between two sides called
Vertex
What do you call the distance around a polygon
Perimeter
How do you calculate perimeter of a polygon?
Add the lengths of its sides
The area of a polygon is measured in terms of
Square units
What do you call angles located within a polygon?
Interior angles
Number of interiors angles is equivalent to …?
Number of sides
What is the formula for the sum of the interior angles of any polygon?
(N-2)180= sum of the interior angles of a polygon
Where n is equal to the number of sides a polygon contains
What is the sum of an interior angle and an exterior angle?
180
Because together they form a straight line
What is the sum of the exterior angles of a polygon ?
360
What is a diagonal ?
Any line within a polygon that extends between two vertices but is not a sideshow
What is the formula for the number of diagonals
[n(n-3)] / 2
Where n= the number of sides in the polygon
Why should you always label the interior angles of a polygon?
The angles of a polygon always add to a fixed sum
When visualizing shapes it is important to…?
Recognize every possible shape
When working with angles be sure to watch out for …
The shape that has all of its angles defined as it is usually key to solving the problem
Exterior angles are equal to the sum of …
Their two opposite interior angles
When there are multiple shapes always choose which one?
The one in which all angles are labeled
What is the side opposite a right angle in a right Triangle
Hypotenuse
What are the three sides of a right triangle called?
Hypotenuse, leg , leg
What is the measurement of each of the three angles in an equaltiral triangle
60 degrees
What do you know about an isosceles triangle ?
It has two sides of equal length
The angles opposite the equal legs of an isosceles triangles are also equal
What is the pythagorean theorem?
a^2 + b^2 = c^2
Only used for right triangles
How do you solve a sexy pythagorean ( right triangle w long legs ) problem?
x^2 - y^2 = (x+y)(x-y)
Make the unknown side
x^2= c^2 - b^2 = (c + b) (c-b)
What are some examples of common pythagorean triples?
3-4-5 [6-8-10, 9-12-15, 12-16-20 , 15, 20, 25]
5-12-13 [10-24-26]
8-15-17
7-24-25
What do you call a right triangle that has two angles or sides of equal measure
Right isosceles
What are the angle measurements of a right isosceles triangle
90 , 45 , 45
What are the ratios of the sides of a right isosceles triangle?
x: x : x(sq rt 2)
What is the short cut to determining the legs of a right isosceles triangle if the hypotenuse is not written as x sqr rt 2
Divide it by 2
Multiply it by sqr rt 2
I.e. if c = 10
Legs = 5 sqr rt 2
What is the ratio of the lengths of the legs of every 30-60-90 triangle?
x : x sqr root 3 : 2x
If the length of the hypotenuse of a right triangle doubles the length of one of its legs then it is a ….
30-60-90 triangle
Two 30-60-90 triangles make …
An equilateral triangle
Twelve 30-60-90 triangles make up
A hexagon
Every right triangle in a problem is usually
A special right triangle
What is the correlation between the sides and angles of a triangle?
The smallest angle of any triangle is always across from the smallest side
The largest angle of any triangle is always across from the largest side
If two angles are equal the…
The opposite sides are equal
What is the triangle inequality theorem
For a triangle to exist, The length of a given side must be less than the sum of the other two sides but greater than the difference between those two sides
What are the characteristics of a similar triangle?
Equal angles
Or
Proportional sides
What are the corollaries of similar triangles ?
If 2 angles of any 2 triangles are equal, the third angle must be as well
If the angles of any 2 triangles are equal, the sides of those triangles are proportional
If the sides of any 2 triangles are proportional, the angles of those triangles are equal
What is the advanced trick for similar triangles when it comes to area ?
The ratio of the areas of two similar triangles is equal to the square of the ratio of the corresponding sides
I.e. if a triangle is two times as big as another its area will be 2^2 or 4 times as large as its similar triangle
What is the formula for area of a triangle ?
(1/2) X Base X Height
Whats another’s name for height
Altitude
How can you calculate the area of an oddly shaped triangle w/o a clear base or height?
Consider rotating the triangle so that it has a defined horizontal base
… of a triangle is defined as the side that runs perpendicular to the height
Base
…of a triangle is defined as the perpendicular distance from a vertex to the side opposite that vertex
Height (altitude)
Advanced note…
The area of a triangle with sides x and y gets larger as the angle between legs x and y gets closer to 90 degrees
What is an exterior angle?
Any angle formed by extending a side of a triangle .
The addition of an interior angle and an exterior angle is…
180 degrees
An exterior angle is equal to the sum of its …
Two opposite interests angles
What does a triangle with parallel lines signify ?
Similar triangles
If a larger right triangle is split into two smaller tight triangles then…
All three triangles are similar
If the hypotenuse doubles the leg you are working with a … special right triangle
30-60-90
Diagonals of a rhombus always cross at what degree?
90