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###### maths GCSE help ( higher maths question)

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2 years ago

hii! we did our mock a few weeks ago. my teacher gave the whole class a sheet of the questions which the whole class got wrong on the test and allowed us to try again.

there was one question she didn't go over and i tried to find the answer online to help me solve it but no results came up.

the question is:

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.

thankyou!

there was one question she didn't go over and i tried to find the answer online to help me solve it but no results came up.

the question is:

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.

thankyou!

Reply 1

2 years ago

Original post by harlz_chalamet

hii! we did our mock a few weeks ago. my teacher gave the whole class a sheet of the questions which the whole class got wrong on the test and allowed us to try again.

there was one question she didn't go over and i tried to find the answer online to help me solve it but no results came up.

the question is:

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.

thankyou!

there was one question she didn't go over and i tried to find the answer online to help me solve it but no results came up.

the question is:

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.

thankyou!

For each of those two proportionalities you should be able to write down an equation involving a constant of proportionality. Then eliminate y between the two.

Have a go and see what you can do.

Reply 2

2 years ago

Original post by ghostwalker

For each of those two proportionalities you should be able to write down an equation involving a constant of proportionality. Then eliminate y between the two.

Have a go and see what you can do.

Have a go and see what you can do.

i get that:

x=ky^2

y=kz^3

and then i would substitute the numbers in. but i don't understand what i would do after.

so

32=ky^2

y=k2^3

y=k8

Reply 3

2 years ago

Original post by harlz_chalamet

i get that:

x=ky^2

y=kz^3

and then i would substitute the numbers in. but i don't understand what i would do after.

so

32=ky^2

y=k2^3

y=k8

x=ky^2

y=kz^3

and then i would substitute the numbers in. but i don't understand what i would do after.

so

32=ky^2

y=k2^3

y=k8

First off the constant of proportionality will not be the same for the two relationships. So, lets call the first one "k" and the second one "m".

Your first two equations are otherwise correct.

Since we want a relationship between x and z, you now want to combine those two equations and eliminate y.

(edited 2 years ago)

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