Thereare threeplanesof symmetry:one parallelto and halfwaybetweeneachpair of parallelfaces.
LessonSummary
In this lessonwe broughttogetherour earlierconceptsof transformationsand our knowledgeaboutdifferent
kindsof shapesand figures.Thesewerecombinedto enableus to describethe symmetryof an object.
For two-dimensionalfigureswe workedwith:
- line symmetry
- rotationalsymmetry
- pointsymmetry
For three-dimensionalfigureswe definedone additionalsymmetry, whichis a planeof symmetry.
Pointsto Consider
Symmetryseemsto be the preferredformatfor objectsin the real world.Thinkaboutanimalsand plants,
and aboutmicrobesand planets.Thereis a reasonwhy nearlyall built objectsare symmetrictoo. Think
aboutbuildings,and tires,and light bulbs,and muchmore.
As you go throughyour daily life, be alert and awareof the symmetryyou encounter.
LessonExercises
True or false?
- Everytrianglehas line symmetry.
- Sometriangleshaveline symmetry.
- Everyrectanglehas line symmetry.
- Everyrectanglehas exactlytwo lines of symmetry.
- Everyparallelogramhas line symmetry.
- Someparallelogramshaveline symmetry.
- No rhombushas morethan two lines of symmetry.
- No right trianglehas a line of symmetry.