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# Geom 1point4

## by herbison on Apr 07, 2008

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## Geom 1point4Presentation Transcript

• 1.4 Angles and Their Measures Objectives: - Use angle postulates - Classify angles as acute, right, obtuse, or straight
• Angles
• An angle consists of two different rays that have the same initial point.
• The rays are the sides of the angle.
• The initial point is the vertex of the angle.
A B C
• Naming Angles
• Name the angles in the figure:
• The measure of angle A is denoted by m _ A
• The measure can be approximated with a protractor using units called degrees. (º)
F G H I
• Congruent
• Angles that have the same measure are called congruent angles .
• Measures are equal, angles are congruent.
• If angles BAC and DEF are both 50º, then the measure of the angles are equal, but the angles are congruent.
• Protractor Postulate
• Look at the picture on the top of page 27.
• Consider a point A on one side of line OB. The rays of the form Ray OA can be matched one to one with the real numbers for 0 to 180.
• The measure of Angle AOB is equal to the absolute value of the difference between the real numbers for Ray OA and Ray OB.
• Angle Terms
• A point is in the interior of an angle if it is between points that lie on each side of the angle.
• A point is in the exterior of an angle if it is not on the angle or in its interior.
• Angle Addition Postulate
• If P is in the interior of _ RST, then
• m _ RSP + m _ PST = m _ RST
• Example
• Look at the horse on the bottom of page 27
• Wearing blinkers, each eye can see 100º. The angle of vision that is seen by both eyes is 60º. Find the angle of vision seen by the left eye alone.
• Classifying angles
• Acute angles measure less than 90º
• Right angles measure 90º
• Obtuse angles measure more than 90º
• Straight angles measure 180º
• Adjacent angles
• Two angles are adjacent angles if they share a common vertex and side, but have no common interior points
• Do page 29, 1-22 together
• Homework:
• Worksheets