Rearranging Formulae

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Rearranging Formulae
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Things to remember

• Dont rush it. You must go through each stage of
  your method and not try to skip any.
• If you are making x the subject it means that you
  want to end up with x and this is the only x
  in your answer.
• Whatever you do to one side of the equals sign
  you must do to the other.

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Example

• Rearrange the formula a x .to make x
  the subject.

Method -
ad dx cx
multiply both sides by d
rearrange to get xs on the left
dx cx ad
x(d c) ad
factorise
divide by (d c)
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Example

• Rearrange the formula a .to make p
  the subject.

Method -
apq q p
multiply both sides by pq
rearrange to get ps on the left
apq p q
p(aq 1) q
factorise
divide by (aq 1)
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Example

• Rearrange the formula a b .to make p
  the subject.

Method -
a b
a(1 p) b(1 p) c
multiply both sides by 1 p
expand brackets
a ap b bp c
ap bp b c a
rearrange to get ps on the left
factorise
p(a b) b c a
divide by (a b)
p
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Example

• Rearrange the formula s b .to make t
  the subject.

Method -
s b
s b
subtract b from both sides
square both sides
(s b)²
(s b)²
rearrange to get t on the left
multiply by p
t p(s b)²