Teacher's Guide - Pearson

Exercise 12.1 (Student’s Book page 210)1 a) Perimeter 5 2 3 30 1 2 3 605180 cmb) h 15 ​√ __________(30 2 225 2 ) ​ 5 16.58 cmh 25 ​√ ___________(60 2 2 25 2 ) ​ 5 54.54 cm∴ h 11 h 25 71.12Area 5 ​1__ ​(a 3 b)25 ​1__ ​ (50 3 71.12)25 1 778 cm 2c) Length 5 71.12 1 2(25) cm5 121.12 cmd) and e) Cost 5 ____ ​122100 ​ 3 ____ ​ 8.50 ​ 1 ______ ​ 1 778 ​ 3 121 10 0005 P12.50Note: It is important for students to understand that a length of 121.12 cm willmost likely be rounded off to 122 cm (in some cases hardware stores may cut onlyhalf-metre lengths and Thsepo might have to buy 1.5 metres, but for the purpose ofthis calculation we assume that he can buy 1.22 metres). Students must also realisethe importance of converting the measurements to metres and m 2 , and of coursethey must know how to do such conversions, i.e. why we divide by 100 in the onecase but by 10 000 in the next.2. a) Perimeter 5 2πr5 2π 3 10 62.8 mb) Cost 5 62.8 3 55.50 5 P3 485.40Investigation (Student’s Book page 211)AC1. ___DF ​ 5 ___ ​ 105 ​ 5 2 ___ ABDE ​ 5 ​ 6__3 ​ 5 2 ___ BCEF ​ 5 ​ 8__4 ​ 5 2ACTherefore ​ ___DF ​ 5 ___ ​ ABDE ​ 5 ___ ​ BCEF ​ 5 22. Perimeter of triangle DEF 5 12 cm and perimeter of ABC 5 24 cmperimeter ABCThe ratio 5 2. The ratios of sides and perimeters are the same.perimeter DEF3. Area of DEF 5 6 cm 2 and area of ABC 5 24 cm 2area ABCThe ratioarea DEF 5 ___ ​ 246 ​ 5 4 5 22 . The ratio of the area is the square of theratio of the side lengths.Chapter 12: Area and perimeter65