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.”
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.
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.