Presentation on theme: "Properties of Triangles"— Presentation transcript:
1 Properties of Triangles Objectives:Identify isosceles, equilateral and right-angledtriangles.Use the word ‘congruent’ when triangles areidentical.Show that the angles of a triangle add up to 180oand use this to find angles.Show that the exterior angle of a triangle is equalto the sum of the interior opposite angles.Use angle properties of isosceles, equilateraland right-angled triangles.
2 Properties of Triangles What do these symbols mean?right angleparallel to each other,but not parallel withthe sides with onlyone arrowparallel toeach othersame lengthas each othersame length as eachother, but not the samelength as the sides withonly one dash
3 Properties of Triangles What are the names and properties of these triangles ?Isosceles:2 sides the same length2 angles the sameEquilateral:All sides the same lengthAll angles the same (60o)Right-angled:Sides can be any lengthOne angle 90oScalene:All the sides are different lengthsAll the angles are different
4 Properties of Triangles Congruent: means all angles and lengths are the same.It can be a rotationeajgfdibhcWhich shapes are congruent?
5 Properties of Triangles Proof that the internal angles in a triangle add up to 180oabAdd a line parallel to one of the sidesAlternate angles are equalThe internal anglesare now on astraight line andtherefore mustadd up to 180oaabbCorresponding angles are equal