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A 180 o Protractor

Inside scale from 0 o to 180 o going in an anti-clockwise direction. Outside scale from 0 o to 180 o going in a clockwise direction. A 180 o Protractor. You need to be able to measure an angle to the nearest degree. To help you do this you should always:.

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A 180 o Protractor

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  1. Inside scale from 0o to 180o going in an anti-clockwise direction. Outside scale from 0o to 180o going in a clockwise direction. A 180o Protractor

  2. You need to be able to measure an angle to the nearest degree. To help you do this you should always: 1. Look directly down onto the cross point. (this avoids parallax errors) 2. Always use the protractor in a horizontal manner as shown below. 

  3. 1 0 on the inside so use inside scale 2 0 on the outside so use outside scale Measuring Angles with a 180o Protractor 50o 67o

  4. 3 4 0 on the inside so use inside scale 0 on the outside so use outside scale Measuring Angles with a 180o Protractor 120o 135o

  5. What’s in the box ? 0 on the inside so use inside scale 0 on the outside so use outside scale 1 Measuring Angles with a 180o Protractor 80o 2 55o

  6. 0 on the inside so use inside scale 0 on the outside so use outside scale 3 Measuring Angles with a 180o Protractor 150o 4 165o

  7. Measure each angle in the shapes below. Answer on your worksheet. 2 3 1 6 5 4

  8. Measure each angle in the shapes below. 900 2 3 1 670 670 680 900 900 1120 680 900 460 1120 6 5 4 480 1180 730 1070 900 1010 1010 420 1100 1100 1070 730 Rectangle 3600 Trapezium 3600 Triangle 1800 Parallelogram 3600 Triangle 1800 Pentagon 5400

  9. 1 2 4 3 6 5 Estimating Angles

  10. D E F Naming Angles Angles are named using the three letters that form them. The middle of the three letters is the vertex of the angle (pointy bit) DEF or DÊFor FED or FÊ D

  11. B A O Measuring Angles  AOB = 27o AOC = 122° C A

  12. Obtuse angle (between 90°and 180°) Right Angle (90°) Acute angle (less than 90°) Straight angle (180°) Reflex angle (more than 180°) Types of angle

  13. What’s in the box 2 ? ACB or BCA 1 A * B C D P * R Q S What is the name of the angle marked with *? What type of angle is this? OBTUSE What is the name of the angle marked with *? 2 PQS or SQP What type of angle is this? ACUTE

  14. x 130° O C Complementary angles add up to 90° So the complement of 40° is 50° 1 0 S Supplementary angles add up to 180° The supplement of 40° is 140° Angle Reasons x = 50° Adjacent angles on a straight line sum to 180°

  15. 70° x x 120° 80° 110° x = 70° Vertically opposite angles are equal x = 50° Angles at a point sum to 360°

  16. x 50° x x 70° 50° x = 60° Angles in a triangle sum to 180° x = 50° Base angles of an isosceles triangle are equal x = 60° Each angle in an equilateral triangle is 60°

  17. 110° x transversal 110° x 50° x Angles on Parallel Lines   x = 110°  Corresponding angles on parallel lines are equal    x = 50°  Alternate angles on parallel lines are equal  x = 70°  Co-interior angles on parallel lines sum to 180°  EXTENSION

  18. Types of Triangles (according to sides) Scalene - no equal sides Isosceles - 2 equal sides Equilateral - 3 equal sides Types of Triangles (according to angles) Acute angled triangle - all angles equal Right angled triangle - one 90° angle Obtuse angled triangle - one angle  90°

  19. What’s in the box 3 ? co 125o ao 100o bo 35o a = 55 b = 125 To find c you must use the new fact that in all triangles the three angles add up to 180o c = 65

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