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1.4/1.5 – Measuring Angles & Angle Relationships. Basics of Measuring Angles. Protractor The tool used to measure angles Degrees The most common unit of measure for angles. Postulates. Angle Congruence Postulate If two angles have the same measure then they are congruent.
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Basics of Measuring Angles • Protractor • The tool used to measure angles • Degrees • The most common unit of measure for angles
Postulates • Angle Congruence Postulate • If two angles have the same measure then they are congruent. • If two angles are congruent then they have the same measure
Postulates • Angle Addition Postulate • If point S is in the interior of PQR, then mPQS + mSQR = mPQR • You can add two parts to get the whole thing
Types of Angles • Acute – measures less than 90° • Obtuse – measures more than 90° but less than 180° • Right – measures exactly 90° • Straight – measures exactly 180° • Reflex – measures greater than 180°
Special Angles • Adjacent angles • Two angles that share an endpoint and a common side • Complementary Angles • Two angles whose measures have a sum of 90°
Special Angles • Supplementary Angles • Two angles whose measures have a sum of 180° • Linear Pair • Two adjacent angles that form a straight line
Linear Pair Property • If two angles form a linear pair, then those angles are also supplementary to each other
Supplementary vs. Linear Pair • Similarities: • Both add up to 180° • Both have two angles • Differences: • Linear pair MUST BE ADJACENT • Supplementary doesn’t necessarily have to be adjacent
Perpendicular Lines • Perpendicular Lines create right angles. • Can be formed by segments, lines or rays. • Form congruent adjacent angles
Vertical Angles • Formed by intersecting lines/segments/rays • Angles that share a vertex. • They are opposite each other. • They are non adjacent. • They are congruent.