Download 1.3 Notes

Geometry Lesson 1.3
Learning Target 1.3- I can name and classify angles.
An angle is formed by two rays, or sides, with a common endpoint called the vertex (plural
vertices).
You can name an angle several ways:
 By its vertex
 By a point on each
ray in the vertex
 By a number
∠R
∠SRT
∠TRS
∠1
*You cannot name an angle just by its vertex if the point is the vertex of more than one
angle. In this case, you must use all 3 points to name the angle, and the vertex MUST be in
the middle.
Ex. ∠BAC
∠CAD
∠BAD
The measure of an angle is usually given in degrees. Since there are 360° in a circle, 1° is
1/360 of a circle.
Protractor Postulate- Given AB and a point O on AB, all rays that can be drawn from O can
be put to a one-to-one correspondence with the real numbers from 0 to 180.
*Basically, this means you can use a protractor to measure angles from 0° to 180°.
Types of angles:
Congruent Angles are angles that have the same measure, written as ∠ABC≅∠DEF, marked
on diagram with “arc marks.”
Angle Addition Postulate- If S is in the interior of ∠PQR, then m∠PQS + m∠SQR =m∠PQR
Ex. m∠DEG= 115° and m∠DEF= 48°. Find m∠FEG.
Angle Bisector- A ray that divides an angle into two congruent angles.
Ex: KM bisects ∠JKL, m∠JKM= (4x+6)° and m∠MKL= (7x-12)°. Find m∠JKM.