Common Geometric Interview Preparation Guide

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Pairs of angles formed where two lines intersect. These angles are formed by rays pointing in opposite directions, and they are congruent. Vertical angles come in pairs.

The point on a segment that lies exactly halfway from each end of the segment. The distance from the endpoint of a segment to its midpoint is half the length of the whole segment.

a line segment connecting two points on a circle; not "do re mi"
A line segment whose endpoints are both on a circle. Not a collection of musical notes.
Any segment from one point on a circle to another. Despite what you might think, they aren't all that musical.

A postulate which states that given a point not located on a line, exactly one line passes through the point that is parallel to original line.

the bottom part of fractions; in this case when more than one fraction has the same bottom as all the others

A unit of measure for the size of an angle. One full rotation is equal to 360 degrees. A right angle is 90 degrees. One degree equals radians.

angles that share a side
Two angles that share both a side and a vertex. They stick by each other through and through.

Angles that add up to 90°
Two wrongs don't make a right, but two complementary angles do. They're two angles that add up to 90° exactly.
Two angles that add up to 90°. Two wrongs don't make a right, but two complementary angles sure do.

A ray that shares a common vertex with an angle, lies within the interior of that angle, and creates two new angles of equal measure.

A ray, one of a pair, that shares a common vertex with an angle, lies within the interior of that angle, and creates, with its partner, three new angles of equal measure. Angle trisectors come in pairs.

on the same plane
Used to describe lines or points that are all on the same plane.
Used to describe lines or points that are all on the same plane.

The smaller part of an angle, spanned by the space between the rays that form an angle. Its measure is always less than 180 degrees, and is equal to 360 degrees minus the measure of the exterior angle.

in probability, results that do not overlap with one another (when flipping a coin, if you get a tail, then the complementary event is getting a head)
A pair of mutually exclusive events where the occurrence of one implies the non-occurrence of the other; this is represented by the fact that the respective Venn diagrams for these events do not overlap, and that the two events themselves comprise the entire sample space.

A unit for measuring the size of an angle. One full rotation is equal to 2Π radians. One radian is equal to degrees.

Angles created when a transversal intersects with two lines. Alternate interior angles lie on opposite sides of the transversal, and on the interior of the space between the two lines. That is, they lie between the two lines that intersect with the transversal.

Of the same size. Angles can be congruent to other angles and segments can be congruent to other segments.

The distance from the center of a regular polygon to the midpoint of one side.
The length from the center of a regular polygon to the center of one of its sides. If you look close, it is equivalent to the height of a triangle if you were to slice the polygon into the three-sided shapes.

how two variables relate to each other
The measure of the linear relationship between two variables. Can be positive or negative, depending on which side of the bed it woke up on.
If this is present, then there is an apparent trend in bivariate data. Correlation is generally positive or negative.
A relationship between two variables. They can be low or high, negative or positive, but if two things are correlated, they are more than just casual acquaintances.
When two variables we've measured have some kind of association or relationship between them. It can be positive, negative, or not exist. The last one is the most depressing, naturally.

The amount of space inside the boundary of a closed shape. As in, "there is x room to fit all the aliens inside Area 51."
The amount of space within the boundaries of a two-dimensional shape, reported in square units (like miles2 or feet2). Area is essentially space, but don't go around saying things like "area-ships," "area-cadets," or the "area-bar" on your keyboard.
The two-dimensional space contained by a particular region.
The amount of two-dimensional space that is taken up within a shape's perimeter.
A measurement of surface. It's like the amount of ground a piece of sod will cover, or exactly how much carpet we have to clean after spilling an entire crockpot of chili (oops).
The measure of the amount of space inside a polygon.
The amount of "stuff" inside of a figure. Very technical, we know.

A line or segment that contains the midpoint of a segment.

The larger part of an angle. Were one of the rays of an angle to be rotated until it met the other ray, an exterior angle is spanned by the greater rotation of the two possible rotations. The measure of an exterior angle is always greater than 180 degrees and is always 360 degrees minus the measure of the interior angle that accompanies it. Together, an interior and exterior angle span the entire plane.

when a transversal intersects two lines, these angles are in the same position on each line. When a transversal crosses two parallel lines, corresponding angles are congruent
Two angles that are in the same relative place compared to each of the two lines and the transversal that cuts them. Corresponding angles are congruent if and only if the two lines crossed by the transversal are parallel.
A pair of angles that are in the same place relative to the transversal and their respective parallel line. They're congruent, too.
Two angles that are in the same relative place compared to each of the two lines and the transversal that cuts them. Corresponding angles are congruent if and only if the two lines crossed by the transversal are parallel.

in probability, when there is more than one outcome, which may (taking a second card after a first has been chosen) or may not (throwing two dice at the same time) affect the outcome of the other
These are when more than one event occurs. For instance, instead of picking one card from a deck, you pick two cards and find the likelihood of a King of Hearts and Queen of Diamonds being selected. Things are getting a bit more complicated with this one.
When more than one event happens at once. The lions, tigers, and bears all arrive at the same time? We think you know how that one ends.

A polynomial with two terms. These guys always use the buddy system.
A polynomial with two terms.
A polynomial with only two terms. The expression x – 3 is a binomial, and so is 96x2y + 13,0278,543.
A polynomial with two terms. You can probably guess what trinomial means.
A polynomial with 2 terms. An example would be 5x2 – 3.

A 180 degree angle. Formed by two rays that share a common vertex and point in opposite directions.