MATHEMATICS Estimating and Measuring Angles

Aims of the Lesson By the end of the lesson you should be able to… recognise the type and therefore size range of an angle. estimate the size of an angle to within 10°. measure the size of angle to within 2°.

Estimating Angles Before estimating the size of any angle you need to recognise what type of angle it is… ie. acute, right, obtuse, straight or reflex and therefore what size it might be… ie. smaller than 90°, between 90° and 180° or between 180° and 360°.

Using Right Angles & Straight Lines Imagine the right angle line (90°) and/or straight lines (180°) Is the angle you are estimating bigger or smaller than these? How much bigger (or smaller)? i.e. What fraction of a right angle? E.g. Half a right angle = 45°

Let’s estimate these angles…

These lines may help…

My estimates… A right angle plus about ½ a right angle I estimate: 90° + 45° = 135° This is about ½ a right angle I estimate: ½ of 90° = 45°

Let’s measure them…

Measuring Angles Turn the paper around so that the left hand line of the angle is horizontal. Now place the left hand side of the baseline of the protractor along the horizontal angle line… AND Ensure that the point of the angle is at the very centre of the protractor’s baseline. Read round from 0° (on the left) in a clockwise direction to where the other angle line is pointing.

Measuring Angles (cont’d) Once you have estimated or measured an angle Check the size matches up with the type of angle! Angle 1 was visibly ‘obtuse’ (i.e °) I estimated it as 135° and measured it as 140° Angle 2 was visibly ‘acute’ (i.e. < 90°) I estimated it as 45° and measured it as 46° Estimates can be up to 10° either side of the actual value, but measures need to be within 2°!

What next? Print out the notes called Angle2a-Est. Read through them and complete the tasks. Work through the MyMaths lesson called Measuring Angles found at: Print out the notes called Angle2b-Meas. Read through them and complete the tasks. Work through the MyMaths online homework called Measuring Angles found at: Now move on to the Angle3 powerpoint