The circumference of a circle is the distance around the circle (its perimeter). You can find the circumference if you know either the radius or the diameter.

Read MoreA **reflection** is a type of transformation that flips a figure over a line. The line is called the **line of reflection**, or the mirror line, and the line of reflection can be horizontal, vertical, or diagonal.

Vertical angles are angles in opposite corners of intersecting lines. So vertical angles always share the same vertex, or corner point of the angle. They’re a special angle pair because their measures are always equal to one another, which means that vertical angles are congruent angles.

Read MoreThere’s a special relationship between two secants that intersect outside of a circle. The length outside the circle, multiplied by the length of the whole secant is equal to the outside length of the other secant multiplied by the whole length of the other secant.

Read MoreIn a pair of similar triangles, corresponding sides are proportional and all three angles are congruent. This means if you know two triangles are similar to one another you can use the information to solve for missing parts.

Read MoreThe **midsegment** in a triangle is a line drawn across the triangle from one side to another, parallel to the side it doesn’t touch. The difference between any other side-splitting segment and a midsegment, is that the midsegment specifically divides the sides it touches exactly in half.

In this lesson we’ll look at the angles formed when a pair of parallel lines is crossed by another line, called a “transversal.” When transversals cross parallel lines, they form angles with special angle relationships.

Read MoreTranslation vectors translate figures in two-dimensional space, from one location to another. The initial point and terminal point of the translation vector are irrelevant. What matters is the length of the vector and the direction in which it points.

Read MoreIn this lesson we’ll look at different types of triangles and how to use Pythagorean inequalities to determine what kind of triangle we have based on their angle measures and side lengths.

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