Cambridge International Mathematics

Formulae and simultaneous equations (Chapter 7) 151

Example 2

Makey the subject

of 2 x+3y=12:

2 x+3y=12

) 2 x+3y¡ 2 x=12¡ 2 x f¡ 2 xfrom both sidesg

) 3 y=12¡ 2 x

)

3 y

3

=

12 ¡ 2 x

3

f¥both sides by 3 g

) y=

12

3

¡

2 x

3

=4¡^23 x

Example 3

Makey the subject

of x=5¡cy.

x=5¡cy

) x+cy=5¡cy+cy f+cyto both sidesg

) x+cy=5

) x+cy¡x=5¡x f¡xfrom both sidesg

) cy=5¡x

)

cy

c

=

5 ¡x

c

f¥both sides bycg

) y=

5 ¡x

c

Example 4

Makez the subject

of c=

m

z

.

c=

m

z

) c£z=

m

z

£z f£both sides byzg

) cz=m

)

cz

c

=

m

c

f¥both sides bycg

) z=

m

c

EXERCISE 7B.1

1 Makeythe subject of:

a 2 x+5y=10 b 3 x+4y=20 c 2 x¡y=8

d 2 x+7y=14 e 5 x+2y=20 f 2 x¡ 3 y=¡ 12

2 Makexthe subject of:

a p+x=r b xy=z c 3 x+a=d

d 5 x+2y=d e ax+by=p f y=mx+c

g 2+tx=s h p+qx=m i 6=a+bx

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Y:\HAESE\IGCSE01\IG01_07\151IGCSE01_07.CDR Tuesday, 28 October 2008 4:28:59 PM PETER