Cambridge International Mathematics

Formulae and simultaneous equations (Chapter 7) 155

6 The perimeter of a polygon is the sum of the lengths of its sides. Write a formula for the perimeterP

of the following shapes:

a i ii iii

b i ii iii iv

Example 8 Self Tutor

Makexthe subject of ax+3=bx+d:

ax+3=bx+d

) ax+3¡bx=bx+d¡bx fsubtractingbxfrom both sidesg

) ax+3¡bx=d

) ax+3¡bx¡ 3 =d¡ 3 fsubtracting 3 from both sidesg

) ax¡bx=d¡ 3 fwriting terms containingxon LHSg

) x(a¡b)=d¡ 3 fxis a common factor on LHSg

)

x(a¡b)

(a¡b)

=

d¡ 3

(a¡b)

fdividing both sides by(a¡b)g

) x=

d¡ 3

a¡b

Example 9 Self Tutor

Maketthe subject of s=^12 gt^2 where t> 0.

1

2 gt

(^2) =s frewrite witht (^2) on LHSg
) gt^2 =2s fmultiplying both sides by 2 g
) t^2 =
2 s
g
fdividing both sides bygg
) t=
r
2 s
g
fas t> 0 g
D MORE DIFFICULT REARRANGEMENTS [2.5]
5m
4m 4m
am
bm
am
3cm
4cm
5cm
xcm
4cm
5cm
xcm
ycm
5cm
xcm
ycm
zcm
IGCSE01
cyan magenta yellow black
(^05255075950525507595)
100 100
(^05255075950525507595)
100 100
Y:\HAESE\IGCSE01\IG01_07\155IGCSE01_07.CDR Wednesday, 17 September 2008 10:09:51 AM PETER