x is directly proportional to the square of y.

y is directly proportional to the cube of z.

z = 2 when x = 32

Find a formula for x in terms of z

y is directly proportional to the cube of z.

z = 2 when x = 32

Find a formula for x in terms of z

Scroll to see replies

Original post by esam 01

x=ky^2

EDIT - it is against forum rules to post a solution ...

I don't agree with esam 01's answer but I could be wrong. What do you have so far @sleepycatash?

Original post by cmbh951

I don't agree with esam 01's answer but I could be wrong. What do you have so far @sleepycatash?

The mark scheme says its x=1/2 z^6 but i don't know how to get there

Original post by sleepycatash

The mark scheme says its x=1/2 z^6 but i don't know how to get there

i ended up with the same answer but z power 3 not 6

Original post by sleepycatash

The mark scheme says its x=1/2 z^6 but i don't know how to get there

A hint is to think about what directly proportional means. Can you write x and y in an equation together if you know that x is directly proportional to the square of y?

Original post by sleepycatash

x is directly proportional to the square of y.

y is directly proportional to the cube of z.

z = 2 when x = 32

Find a formula for x in terms of z

y is directly proportional to the cube of z.

z = 2 when x = 32

Find a formula for x in terms of z

Post your working and ignore what others have posted

Original post by esam 01

this is not the solution

You've tried to work through the problem - that's against the rules EDIT please

Original post by cmbh951

A hint is to think about what directly proportional means. Can you write x and y in an equation together if you know that x is directly proportional to the square of y?

x=ky^2

y=cz^3

x=k(cz^3)^2

x=kc^2z^6

32=kc^2 2^6

32=64kc^2

1/2= kc^2

(edited 1 year ago)

Original post by Muttley79

Post your working and ignore what others have posted

I hope I'm not included in "others" when I'm giving a genuine hint and not the full (incorrect) solution.

Original post by sleepycatash

x=ky^2

y=cz^2

y=cz^2

Looks good, but y is directly proportional to the cube of z, not the square.

Now if we know what z is when we know what x is, we would want an equation involving only x and z.

Is my edit the right working? Am I on the right track?

Original post by sleepycatash

Is my edit the right working? Am I on the right track?

Yep, you've got it. So going back to your formula for x in terms of z, is there a nicer way to write it?

Original post by cmbh951

Yep, you've got it. So going back to your formula for x in terms of z, is there a nicer way to write it?

Would it be x=1/2 z^6

Original post by sleepycatash

Would it be x=1/2 z^6

yes

most excellent

Original post by sleepycatash

Would it be x=1/2 z^6

That's it a nice check is to put your values of x and z back into the formula and see if it works.

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