Gcse maths help- how do i solve this

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Alstudent02
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#1
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#1
Y is inversely proportional to x2 (squared) and y = 3 when x=12

Show that y= 27 when x =4
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Patpsbl
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#2
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#2
inversely proportional means that what you do to x is the opposite to what you do to Y. I can't exactly remember the working out (I haven't done maths in two years) so I can't help you with that but hopefully I helped a little
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flaurie
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#3
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#3
(Original post by Alstudent02)
Y is inversely proportional to x2 (squared) and y = 3 when x=12

Show that y= 27 when x =4
what's your working so far?
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emfileman
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#4
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#4
inversely proportional means that y is proportional to 1/x^2 (x^2=x squared)
y=k/x^2
3=k/144
k=432 (constant of proportionality)

27=432/4^2
27=432/16
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flaurie
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#5
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#5
  • y ∝ 1/x
  • y = k/x
  • So xy = k

if this helps? Try substituting the numbers in
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flaurie
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#6
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#6
(Original post by emfileman)
inversely proportional means that y is proportional to 1/x^2 (x^2=x squared)
y=k/x^2
3=k/144
k=432 (constant of proportionality)

27=432/4^2
27=432/16
try not to give full answers, let them work it out with some guidance, otherwise they don't learn anything
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DominicW123
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#7
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#7
Y is inversely proportional to x^2 so Y= k/x^2You can rearrange that to be k = Y times x^2, therefore, k=3 times 12^2 which is 432.Now, to prove that y = 27 when x = 4 we do 432/4^2 which is in fact 27!
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Olliewaitroselad
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#8
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#8
You should've done this in class but inversely proportional means y =k/x*. you needs to sub in your x and y values to work out k. 3 = k/12* so therefore,
k=144x3=432
so y = 432/x, when y = 27, 27 = 432/x*.
X* = 432/27
X* = 16
x=4

Hope that helped
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