2.1 Naming and Measuring Angles
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- An angle is formed by two rays or sides with a common endpoint called the vertex. Angles can be named using the vertex and endpoints, just the vertex if unique, or a number. - Angles are classified as acute (<90°), right (90°), or obtuse (>90° and <180°). A straight angle is 180°. - Congruent angles have the same measure. Their measures can be indicated with arc marks or the lowercase "m" notation.
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2.1 Naming and Measuring Angles
- 1. Naming and Measuring Angles The student will be able to (I can): • Correctly name an angle • Classify angles as acute, right, or obtuse
- 2. angle – a figure formed by two rays or sides with a common endpoint. Example: vertex – the common endpoint of two rays or sides (plural: vertices). Example: A is the vertex of the above angle ● ● A C R
- 3. Notation: An angle is named one of three different ways: 1. By the vertex and a point on each ray (vertex must be in the middle) : TEA or AET 2. By its vertex (if only one angle): E 3. By a number: 1 Methods 1 and 3 are always correct. Method 2 can only be used if there is only one angle at that vertex. ● ● ● E T A 1
- 4. Example Which name is not correct for the angle below? TRS SRT RST 2 R ● ● ● S R T 2
- 5. Example Which name is not correct for the angle below? TRS SRT RST 2 R ● ● ● S R T 2
- 6. acute angle – an angle whose measure is greater than 0° and less than 90°. right angle – an angle whose measure is exactly 90°. obtuse angle – an angle whose measure is greater than 90° and less than 180°.
- 7. straight angle – an angle whose measure is exactly 180° (also known as opposite rays, or a line) ● ● ●
- 8. congruent angles – angles that have the same measure. mWIN = mLHS WIN LHS Notation: “Arc marks” indicate congruent angles. Notation: To write the measure of an angle, put a lowercase “m” in front of the angle bracket. ● ● ● ● ● ● L H S W I N mWIN is read “the measure of angle WIN”