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