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Geometry Unit

Geometry Unit. Day 2 Notes- Angles. What is an Angle?. Two rays that share the same endpoint form an angle. The point where the rays intersect is called the vertex of the angle. The two rays are called the sides of the angle. How are angles named?.

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Geometry Unit

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  1. Geometry Unit Day 2 Notes- Angles

  2. What is an Angle? • Two rays that share the same endpoint form an angle. The point where the rays intersect is called the vertex of the angle. The two rays are called the sides of the angle.

  3. How are angles named? • We can name an angle by using a point on each ray and the vertex. The angle below may be specified as angle ABC or as angle CBA; you may also see this written as ABC or as CBA. Note how the vertex point is always given in the middle.

  4. Degrees: Measuring Angles • We measure the size of an angle using degrees. • We use a tool called a protractor to measure angles.

  5. Types of angles • Angles are classified by their measures. There are 4 types of angles:

  6. Acute Angles • An acute angle is an angle measuring between 0 and 90 degrees

  7. Obtuse Angles • An obtuse angle is an angle measuring between 90 and 180 degrees.

  8. Straight Angles • A straight angle is an angle measuring 180 degrees. It looks like a straight line.

  9. Right Angles • A right angle is an angle measuring 90 degrees.

  10. Using a protractor • A protractor is used to measure angles.  In this section, we will consider the use of a protractor that has the shape of a semi-circle and two scales marked from 0º to 180º. • The two scales make it easy for us to measure angles facing different ways. • To measure the size of an angle, place the protractor over the angle so that the center of the protractor is directly over the angle's vertex, and the base line of the protractor is along the • arm, of the angle.

  11. Complementary Angles • Two angles are complementary if the sum of their measures is 90o • Angle ABC = 90o • Angle ABD = 55o • Angle DBC = ? • To find this out we Subtract 90-55=35o. So Angle DBC = 35o A D 55o ? B C

  12. Supplementary Angles • Two angles are supplementary if the sum of their measures is 180o. Angle ABD = 180o Angle ABC = 155o Angle CBD = ? To find the measure of angle CBD, you subtract the angle we know from the total, or 180 – 155. So, Angle CBD = 180-155 or 25o. C B A D

  13. Practice • http://www.crickweb.co.uk/assets/resources/flash.php?&file=angle • http://www.mathplayground.com/alienangles.html

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