OCR GCSE MATHS 9.1 ANGLE FACTS

9.1 Angle facts ©Cambridge University Press and OCR 2020 1 9 Angles 9.1 Angle facts None of the diagrams on this worksheet are to scale. • angles around a point • angles on a straight line • vertically opposite angles. TIP Symbols can be used to label and refer to angles. For example, we could refer to the angle below as or or x. WORKED EXAMPLE Angles around a point total 360° Work out the size of the angle marked x in the diagram and state whether it is acute, obtuse or reflex. Solution Angles around a point total 360°, so x + 50 = 360 x = 360 − 50 x = 310° Remember: • an acute angle is smaller than 90° • an obtuse angle is between 90° and 180° • a reflex angle is between 180° and 360°. So angle x is a reflex angle. 9.1 Angle facts ©Cambridge University Press and OCR 2020 2 Exercise 1 1 Calculate the size of the lettered angle in each diagram and state whether it is acute, obtuse or reflex. a b c d e f 2 Calculate how many degrees the hour hand of a clock turns between midday and 5p.m. on the same day. 3 Calculate how many degrees the minute hand of a clock turns between 9.15 a.m. and 9.40 a.m. TIP Angles on a straight line total 180°. Remember, the symbol for a right angle is: 4 Calculate the size of the lettered angles. a b c 5 Explain why AE cannot be a straight line