Triangles
WHAT IS A TRIANGLE?
A triangle is: A polygon A three sided figure A geometric shape with three angles or vertices
HOW CAN WE CLASSIFY THEM? What does “classify” mean? to sort or group together By their angles By their sides
Can be classified by their congruent sides Triangles Can be classified by their congruent sides
Scalene Triangle no congruent sides
Has at least two congruent sides Isosceles Triangle Has at least two congruent sides
Has three congruent sides Equilateral Triangle Has three congruent sides
Can be classified by the measurement of their angles Triangles Can be classified by the measurement of their angles
Right Triangle Has one right angle
Acute Triangle Has three acute angles
Triangle with one obtuse angle Obtuse Triangle Triangle with one obtuse angle
Cut a triangle out of the sheet of paper from Mrs. Burt Triangles Cut a triangle out of the sheet of paper from Mrs. Burt
Put them together on a straight line. Triangles Tear off the dotted corners. Piece them together by having the corners touch. Put them together on a straight line.
The sum of the angles of a triangle is ALWAYS Triangles The sum of the angles of a triangle is ALWAYS 180 degrees -a straight line-
To find a missing angle, add up the two angles you know Triangles To find a missing angle, add up the two angles you know
? 70˚ 70˚
Subtract the sum from 180 and you have the missing angle Triangles Subtract the sum from 180 and you have the missing angle
40˚ ? 70˚ 70˚
Congruent Triangles
Congruent Triangles Have the same SIZE and the same SHAPE They may be flipped or rotated
ABC is congruent to DEF B F E D A C
One for you Name the congruent triangles remembering to name the angles in order F E Z means “is congruent to” D ZXY ~ FED = Y X