Geometry Glossary - P

Parallelogram:

see quadrilateral    see congruent

Parallelepiped:

a prism whose bases are parallelograms

Parallel Line:

two lines, which lie in the same plane and are at all points equidistant from each other

Parallel Planes:

two planes that are at all points equidistant from each other

Pentagon:

a polygon with five sides

 

Perimeter:

the distance around any object; for a polygon, the perimeter is the sum of the measures of the sides; the circumference of a circle is analogous to perimeter; measurement of perimeter is expressed in linear units

Perpendicular bisector:

a line or segment, which intersects a segment at its midpoint to form a right angle

Perpendicular lines:

two lines meeting to form right angles

Pi ():

an irrational number that represents the ratio of the circumference of a given circle to its diameter

Plane ( Undefined Term ):

can be described as an infinite, flat, two-dimensional surface that is named by a script capital letter

Point ( Undefined Term ):

can be described as a zero-dimensional "dot" that is named using a capital letter

Point-slope form of a linear equation:

 y-y¹ =m(x-x¹ )

Polygon:

 a closed curve formed only by line segments that meet at their endpoints (called vertices)

see also: simple closed curve

Polygonal region:

 the union of a polygon and its interior

Polyhedron:

literally "many faces"; it is the union of four or more polygons meeting at their edges and enclosing a single space

 

Postulate:

 a statement accepted as true without proof; synonymous to an axiom

Prism:

a polyhedron with two congruent parallel bases and lateral faces that are parallelograms; a prism is named by the shape of its bases; for example, a triangular prism has congruent triangles for its bases

Prismatoid:

a polyhedron resembling a prism (two bases in parallel planes); however, its bases need not be congruent, nor even the same type of polygon; all of its vertices in two parallel planes and its lateral faces are quadrilaterals and/or triangles

Prismoid:

a prismatoid with two similar, but not congruent, bases; its lateral faces are trapezoids

Protractor:

 an instrument used to measure an angle; typical scale units are degrees

Pyramid:

a polyhedron with one base and triangular lateral faces; A pyramid "comes to a point" and is named for the shape of its base - below is pictured a pentagonal pyramid

Pythagorean Theorem:

in a right triangle, the sum of the squares of the measure of the legs of the triangle are equal to the square of the measure of the hypotenuse