Characteristics and Properties of Shapes

     I think when introducing two-dimensional figures, I would first present a list of them to my students.  I would start the lesson by having them define as many of them as possible.  They could write a definition, draw a picture, or list examples of the figures.  This activity would allow me to determine what prior knowledge my students have of two-dimensional figures.  Next, as a class the students would share their definitions with one another, and we would nail down appropriate definitions.

 

Concave- when drawing diagonals on a concave figure, at least one is outside of the shape

 Convex – when drawing diagonals on a convex figure, all of them are inside of the shape

  Visit this websit to see pictures:

http://www.mathsisfun.com/geometry/polygons.html

 

Polygon – a shape that is closed and has straight sides

 

 

Regular Polygon – a shape that has sides of the same length and equal angle measurements

 

 

Equilateral Triangle – triangle whose sides are of equal length

 Isosceles Triangle – triangle having two sides of equal length

 Scalene Triangle – triangle having no sides of equal length

 Right Triangle – has one angle measuring 90°

 Obtuse Triangle – has one angle measuring more than 90°

 Acute Triangle – has 3 angles all measuring less than 90°

  For pictures of  triangles visit site:

 http://www.mathsisfun.com/triangle.html

Parallelogram – is a quadrilateral having two pairs of parallel sides

 

 

Rhombus – is a parallelogram with 4 sides of equal length

 

 

Rectangle – is a parallelogram that has four right angles; opposite sides are of equal length

 Square – is a parallelogram with 4 sides of equal length and 4 right angles

Visit this site for pictures:

http://www.mathsisfun.com/quadrilaterals.html

Parallel

Parallel – two lines that run side by side and will never intersect

This definition is as I remember learning it as a child.

Parallel – extending in the same direction, everywhere equidistant, and not meeting http://www.merriam-webster.com/dictionary/parallel

http://library.thinkquest.org/20991/geo/parallel.html

Example:  http://math.about.com/od/geometry/ss/linessegments_6.htm

Perpendicular

Perpendicular – lines that intersect and form 4 right angles

This definition is based on prior knowledge – I remember that perpendicular lines form four 90 degree angles

A line is perpendicular to another if it meets or crosses it at right angles (90°). http://www.mathopenref.com/perpendicular.html

Example: 

http://math.about.com/od/geometry/ss/linessegments_5.htm