Proportionality question

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Peanut247
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#1
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#1
How do you do this type of question?Image
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davros
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#2
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#2
(Original post by Peanut247)
How do you do this type of question?Image
Do you know how to rewrite a statement like "x is directly proportional to the square of z" in terms of indices and some unknown constant(s)?
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Peanut247
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#3
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(Original post by davros)
Do you know how to rewrite a statement like "x is directly proportional to the square of z" in terms of indices and some unknown constant(s)?
x [directly proportional to] k(z^2)
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TenOfThem
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#4
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#4
(Original post by Peanut247)
x [directly proportional to] k(z^2)
x = kz^2
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davros
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#5
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(Original post by Peanut247)
x [directly proportional to] k(z^2)
Not quite - see TenOfThem's correction!

Now you should be able to write something similar for the case of inverse proportion
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Peanut247
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#6
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#6
(Original post by davros)
Not quite - see TenOfThem's correction!

Now you should be able to write something similar for the case of inverse proportion

y=1/(z^3)
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TenOfThem
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#7
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#7
(Original post by Peanut247)
y=1/(z^3)
y = \dfrac{k}{z^3}
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davros
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#8
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(Original post by Peanut247)
y=1/(z^3)
Again, see TenOfThem's correction - you missed out the constant!!

Now you just need to combine these things in various ways
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Peanut247
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#9
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(Original post by davros)
Again, see TenOfThem's correction - you missed out the constant!!

Now you just need to combine these things in various ways
This was the bit I got stuck on.. I tried making them both equal z but just flopped!
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Peanut247
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#10
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#10
(Original post by TenOfThem)
y = \dfrac{k}{z^3}
Thank you :P
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TenOfThem
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#11
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#11
(Original post by Peanut247)
This was the bit I got stuck on.. I tried making them both equal z but just flopped!
Try making them both z^6
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Peanut247
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#12
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#12
(Original post by TenOfThem)
Try making them both z^6
y=k/z^3 becomes 1/y^2 = kz^6

x=kz^2 becomes x^3 = kz^6

So x^3 = 1/y^2 making the answer D?
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TenOfThem
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#13
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#13
(Original post by Peanut247)
y=k/z^3 becomes 1/y^2 = k^2z^6

x=kz^2 becomes x^3 = k^3z^6

So x^3 = k/y^2 making the answer D?
But, yes, D
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