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## Basic Geometry

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**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.