Basic Geometry Vocabulary Review

Plane and Solid Figures Plane figure – a plane figure has just 2 dimensions – length and width. Solid figure – a solid figure has 3 dimensions – length, width, and height.

Solid Figures Face – each flat surface of a solid figure Edge – a line segment where 2 faces meet on a solid figure. Vertex – “a corner” – where 3 or more edges meet. The plural form of vertex is “vertices.”

Solid Figures

Polygons Polygon – a polygon is a closed plane figure made up of line segments. Each line segment is a side.

Polygons – Know Your Prefixes! “Tri” – means 3 – a triangle has 3 sides. “Quad” – means 4 – a quadrilateral has 4 sides. “Penta” – means 5 – a pentagon has 5 sides. “Hexa” – means 6 – a hexagon has 6 sides. “Octa” – means 8 – an octagon has 8 sides. “Nona” – means 9 – a nonagon has 9 sides. “Deca” – means 10 – a decagon has ten sides.

Points, Lines, Line Segments, and Rays Point – an exact location in space. Line – a straight path of points that goes on and on in two directions. Line segment – a part of a line. It has 2 endpoints. Ray – part of a line. It has one endpoint and continues on and on in only one direction.

Angles Right angle – has a square corner Acute angle – less than a right angle Obtuse angle – more than a right angle. Straight angle – forms a straight line.

Lines Parallel lines – never intersect. Intersecting lines – lines that cross through the same point. Perpendicular lines – lines that form right angles where they intersect each other.

Triangles We learned that there are 2 ways to classify (or group) triangles. One way is to classify (or group) triangles by the length of their sides. The second way is to classify (or group) them is by their angles. Length of sides – Equilateral, isosceles, or scalene. By their angles – right, acute, or obtuse.

Equilateral Triangles Equilateral triangles – all 3 sides have the same length.

Isosceles Triangle Isosceles triangle – 2 of the sides have the same length. You can see that the base (or bottom) of the triangle is shorter than the 2 sides. However, the 2 sides are the same length.

Scalene Triangle Scalene triangle – none of the 3 sides are the same length.

Right Triangle Right Triangle – 1 angle of the triangle is a right angle.

Acute Triangle Acute triangle – all 3 angles of the triangle are acute angles. Remember – if all 3 sides are the same length (equilateral), the triangle is automatically an acute triangle!

Obtuse Triangle Obtuse triangle – if one of the angles of the triangle makes an obtuse angle, the triangle is an obtuse triangle.

Quadrilaterals Quadrilaterals can also be classified (or grouped) by their angles or their pairs of sides! Remember , quad means 4! So we are talking about 4 sided figures!

Rectangle Rectangle – there are 4 right angles!

Square Square – there are 4 right angles and all sides are the same length.

Trapezoid Trapezoid – There is only one pair of parallel sides.

Parallelogram Parallelogram – opposite sides are parallel.

Rhombus Rhombus – opposite sides are parallel AND all 4 sides are the same length.

Circles Circles – we learned that circles are different from other plane figures because they have no sides. A circles is a closed plane figure made of all the points in the same distance from a point called the center.

Center of the Circle

Radius Radius – is any line that segment that connects the center to a point on the circle.

Diameter Diameter – is any line segment that connects two points on the circle and passes through the center.

Chord Chord – is any line segment that connects two points on a circle.

Circumference of a Circle Circumference – the distance around the outside of a circle. The circumference of a circle is calculated by multiplying pi (3.14) times the diameter of the circle.

Congruent Congruent – same shape, same size.

Slide (Translation) Slide (translation) – moves a figure in a straight direction.

Flip (Reflection) Flip (reflection) – a figure gives its mirror image.

Turn (Rotation) Turn (rotation) – moves a figure around a point.

Symmetry Symmetry – when a figure can be folded into two congruent halves. *Means one half can lay perfectly over the other half in an exact match. line of symmetry

Similar Similar – same shape, but may or may not have the same size! *If items are congruent, they are automatically similar. However, just because items are similar, doesn’t mean they are automatically congruent.

Perimeter Perimeter – the distance around the outside of a figure. Just add the length of all sides together to calculate the perimeter. Real world use of perimeter – building a fence.

Area Area – the number of square units needed to cover the region inside a figure. Multiply the length x width to find the area of a figure. Real world use of area – flooring/carpet. Remember – use “square” in your answer. 32 sq. in.

Volume Volume – the number of CUBIC units needed to fill a solid figure. Multiply the length x width x height to calculate the volume. Real world of volume – Shopping for refrigerator or freezers. Shipping companies like UPS or FedEx. Remember to use “CUBIC” in your answer. 48 cubic inches.