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

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.

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

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

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

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

Measure each angle in the shapes below. Answer on your worksheet

Measure each angle in the shapes below Rectangle Trapezium Triangle Parallelogram Pentagon Triangle 180 0

Estimating Angles

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) E D F  DEF or DÊF or  FED or FÊ D

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

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

What’s in the box 2 ? What is the name of the angle marked with * ? 2 P RQS *  ACB or  BCA What type of angle is this?OBTUSE 1 A BCD * What is the name of the angle marked with * ?  PQS or  SQP What type of angle is this?ACUTE

Complementary angles add up to 90° C O Supplementary angles add up to 180° S1 0 So the complement of 40° is50° The supplement of 40° is140° 130° x x = 50° Adjacent angles on a straight line sum to 180° Angle Reasons

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

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

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

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°

What’s in the box 3 ? 125 o aoao bobo a = b = o 35 o coco c = To find c you must use the new fact that in all triangles the three angles add up to 180 o 65