Cambridge International Mathematics

150 Formulae and simultaneous equations (Chapter 7)

9 Theperiod or time taken for one complete swing of a simple

pendulum is given approximately by T=^15

p

lseconds, wherel

is the length of the pendulum in cm. Find:

a the time for one complete swing of the pendulum if its length

is 45 cm

b the length of a pendulum which has a period of 1 : 8 seconds.

Activity Pizza pricing

#endboxedheading

Luigi’s Pizza Parlour has a ‘Seafood Special’ pizza advertised this week.

LUIGI’S

PIZZAS

Free Delivery!

“Seafood Special”

Small E 8 : 00

Medium E 10 : 60

Large E 14 : 00

Family E 18 : 20

Sasha, Enrico and Bianca decide to find Luigi’s formula for determining his priceEPfor each size pizza.

Lettingrcm be the radius of a pizza, the formulae they worked out were:

Sasha: P=

17 r¡ 27

20

Enrico: P=

r

33 r¡ 235

2

Bianca: P=5+

r^2

40

:

What to do:

In the formula D=xt+p, Dis expressed in terms of the other variables,x,tandp. We therefore say

thatDis thesubjectof the formula.

We can rearrange formulae to make one of the other variables the subject. However, we must do this

carefully to ensure the formulae are still true.

Werearrangeformulae using the same processes which we use to solve equations.

Anything we do to one side we must also do to the other.

B FORMULA REARRANGEMENT [2.5]

Small Medium Large Family

22 cm 30 cm

38 cm 46 cm

l

point of support

pendulum

1

2

Investigate the suitability of each formula.

Luigi is introducing a Party size pizza of

diameter cm. What do you think his

price will be?

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Y:\HAESE\IGCSE01\IG01_07\150IGCSE01_07.CDR Monday, 27 October 2008 9:29:51 AM PETER