This document discusses naming and classifying triangles based on their angles and sides, including acute, right, obtuse, equilateral, isosceles, and scalene triangles. It also provides the formula for calculating the area of a triangle using 1/2 base x height or base x height/2, and notes that the sum of the interior angles of any triangle is always 180 degrees. Examples are given to classify different triangles as isosceles/right or equilateral/acute.

1. lesson 20.notebook September 19, 2013
Lesson 20:
*Naming Triangles...
By angles:
• 3 acute angles­­>acute triangle
• 1 right angle­­>right triangle / 2 acute angles
• 1 obtuse angle­­>obtuse triangle / 2 acute angles
By sides:
• 3 equal sides­­>equilateral triangle / 3 equal angles
• at least 2 equal sides­­>isosceles triangle / 2 equal angles
• no equal sides­­>scalene triangle / no equal angles

2. lesson 20.notebook September 19, 2013
Formula for area of a triangle:
*base height or 1/2(base height)
2
(Base and height must
be perpendicular!!)
*The SUM of the measures
of the angles in a triangle
= 180 degrees

3. lesson 20.notebook September 19, 2013
Examples ­ Lesson 20
pg. 129
A) isosceles triangle & right triangle
B) equilateral triangle & acute triangle
C) obtuse triangle & scalene triangle
D) x =
y =

4. lesson 20.notebook September 19, 2013
E)
F)
G)
H)