Geometry Terms for Mathematics I

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acute angle

Any angle measuring between 0^o and 90^o

When parallel lines are cut by a transversal, a pair of angles that are exterior to the parallel lines on opposite sides of the transversal are congruent

altitude

In a quadrilateral, a segment perpendicular to both bases; in a triangle, a segment perpendicular to the base opposite a vertex of the triangle

area

The number of square units that will cover a surface

base

Any side of a parallelogram that is perpendicular to the height; the two opposite and parallel faces of a prism; the base of a pyramid opposite the vertex

Middle point of a circle equidistant from all points on the circle; middle point of a sphere equidistant from all points on the sphere; or middle point of a regular polygon inscribed in a circle equidistant from all vertices

The set of all points in a plane that are equidistant from the center point

A statistical chart shaped like a circle and used to compare parts of a whole

circular cone

A three-dimensional shape that has one vertex opposite one base

circular cylinder

A three-dimensional shape that has two parallel congruent bases shaped like circles

The perimeter or distance around a circle

congruent figures

Figures that are exactly the same size and shape, with corresponding congruent angles and corresponding congruent sides

Two perpendicular lines that intersect at the zero points to form a plane that includes the x- and y- axes

diameter

The distance across a circle through its center. A chord containing the center of a circle.

Reducing or enlarging a figure

The intersection of two faces of a three-dimensional figure

An acute triangle with three congruent angles measuring 60^o each

A triangle with three congruent sides

Any surface forming the side or base of a prism, pyramid, cone or cylinder

When a list of numbers are related by multiplying the previous number by a constant factor

The weight measurement unit of the metric system

A dot marking a point on the number line or in the coordinate plane

The length of the altitude in a triangle or quadrilateral

In a right triangle, the side opposite the right angle

A linear measurement unit of the customary or standard system

A method of measuring objects using a proportion without measuring the object itself

A triangle with two congruent sides

In a right triangle, either of the two sides intersecting to form the vertex at the right angle

An undefined term in geometry; extends in both directions; has no thickness or width; formed with double arrows

Figures that match point for point when folded in half along a line

A fold line that shows symmetry of a figure

The measurement of length or distance in a straight line

The liquid capacity measurement unit of the metric system

In a triangle, the segment joining the vertex to the midpoint of the side opposite; in a trapezoid, the segment joining the midpoints of the two legs

The linear measurement unit of the metric system

A system of weights and measures based on ten.

Any angle measuring between 90^o and 180 ^o

Any triangle containing one angle measuring between 90^o and 180 ^o

A pair of numbers representing a point on the coordinate plane, listed in parentheses in the order of (x, y). For example: In the ordered pair (3, 4), x = 3 and y = 4

The point on the coordinate plane where the x- and y- axes intersect

Lines that lie in the same plane but do not intersect

A quadrilateral with two pair of opposite sides parallel

A quadrilateral with five sides

Squares of whole numbers. For example: 2² = 2^.2, or 4

Lines that intersect forming right angles at the point of intersection

A closed geometric figure in a plane formed by three or more segments

The smallest unit of measure by a given measuring instrument is its. The smaller the unit, the more precise the measure.

A three-dimensional figure with two congruent and parallel opposite bases in the shape of a polygon

A three-dimensional figure with three or more triangular lateral faces and only one base opposite a vertex

A discovery attributed to Pythagoras in which the square on the hypotenuse equals the sum of the squares on the legs of a right triangle. The formula is written c² = a² + b²

A set of three integers which satisfy the Pythagorean Theorem.

One of the four regions formed by the intersection of the x- and y-axes in the coordinate plane

The symbol used to represent a square root and looks like this: Ö

The distance from the center of a circle to any point on the circle

A parallelogram with four right angles

A prism with rectangular bases

A mirror image of a figure across a line of symmetry

A parallelogram with four congruent sides

The distance from the center of a circle to any point on the circle

Any angle measuring exactly 90^o

A triangle with one angle measuring exactly 90^o

Transformation of a tessellation that involves a turn about the vertices of the base figure

Symmetry obtained by rotating a figure about a fixed point less than 360^o

The ratio of a dilated image to the original image

A triangle with no two sides congruent

Figures having the same shape but may differ in size. The corresponding angles are congruent and the corresponding sides are proportional

Two polygons with corresponding angles congruent and corresponding sides proportional

A three-dimensional figure

A parallelogram with all sides congruent and all angles congruent

One of two equal factors that form a perfect square

The sum of the area of all the faces of a three-dimension figure

Figures that can be folded into two identical parts

A repetitive pattern of polygons that fit together with no holes or gaps

Movement of geometric figures to modify tessellations

To translate a point as described by an ordered pair

A line that cuts or intersects two other lines forming 8 angles

A quadrilateral with exactly one pair of opposite parallel sides

A prism with triangular shaped opposite and parallel bases

The study of triangle measurement

A vertex of a polygon is the point where any two sides intersect. A vertex of a pyramid is the point where all the faces intersect.

The number of cubic units needed to fill a space, such as a prism or cylinder

The horizontal line in the coordinate plane

The first number in an ordered pair, (x, y)

The vertical line in the coordinate plane

The second number in an ordered pair, (x, y)