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parallelogram
A quadrilateral in which pairs of opposite sides are parallel.
perpendicular
Two lines are perpendicular to each other if they intersection at right angles.
perpendicular bisector
The perpendicular bisector of a segment is a line through the midpoint of the segment that is perpendicular to it.
point-slope form
The form of an equation for a line with slope through the point .
pre-image
If a rigid transformation takes to , then is the pre-image and is the image.
radian
To nd the radian measure of an angle, create a circle of any size centered at the vertex of the angle. The angle traces out an arc of the circle. The radian measure of the angle is the ratio of arc length to radius.
rectangle
A quadrilateral with four right angles.
re ection
A re ection is de ned using a line. It takes a point to another point that is the same distance from the given line, is on the other side of the given line, and so that the segment from the original point to the image is perpendicular to the given line.
re ection symmetry
A gure has re ection symmetry if there is a re ection that takes the gure to itself.
regular polygon
A polygon where all of the sides are congruent and all the angles are congruent.
rhombus
A quadrilateral with four congruent sides.
right angle
When you divide a straight angle into two congruent angles, each of the two angles is a right angle. For example, the four corners of a rectangle are right angles.
right prism
A right prism is one whose sides are perpendicular to its base.
rigid transformation
A rigid transformation is a translation, rotation, or re ection. We sometimes also use the term to refer to a sequence of these.
Unit 7 Glossary 127