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Why have formulas?

Area of disc

Speed, Distance, Time

E = mc2

Changing the subject

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• Formulas are designed to make maths easy. • When presented with a new formula, learn

what each letter stands for. Once this is known, the formula can be used.

• The important thing about formulas is to use them without worrying about where the formulas come from. This is what they are produced for.

Why have formulas?Why have formulas?

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r

r

Area of disc = Area of disc = rr22

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D

S T

= 2 m/sec

Speed =Distance Time

= 10 5

Walk 10 metres (m) across the room in 5 seconds.

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EE = = mm cc22

E = energy measured in joules (J)

m = mass measured in kilogrammes (kg)

c = speed of light measured in metres per second (m/s)

Light moves at about 300,000 km/sec!

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––

Changing the subject of a formulaChanging the subject of a formula

E m c2=

Divide both sides by c2

(m)

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––

Changing the subject of a formulaChanging the subject of a formula

E m c=

Divide both sides by m

2

Take the square root of both sides

(c)

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–––––( )

Changing the subject of a formulaChanging the subject of a formula

a + d e=

Multiply both sides by u

2

Take 2f from both sides

+ 2fu

–

Take the square root of both sides

(e)

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Changing the subject of a formulaChanging the subject of a formula

Take ut from both sides

(a)s = ut + at

212–

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Changing the subject of a formulaChanging the subject of a formula

Multiply both sides by 2

(a)s – ut = at

212–

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Changing the subject of a formulaChanging the subject of a formula

Divide both sides by t

2

(a)2(s – ut) = at

2

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Changing the subject of a formulaChanging the subject of a formula

Multiply out top line

(a)–––––––2(s – ut)

= at

2

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Changing the subject of a formulaChanging the subject of a formula

Simplify

(a)––––––– 2s – 2ut

= at

2

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Changing the subject of a formulaChanging the subject of a formula

(a)t

2 t = a–– – –– 2s 2u

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