Question

The variables y and x^2 are directly

proportional. It is given that the difference
between the values of ý when x = 2 and x = 5
is 20. Form an equation relating y and x.

Answer 1

y =
`(20)/(21)` x²

Explanation:

Given that y and x² are directly proportional then the equation relating them is

y = kx² ← k is the constant of proportion

When x = 2

y = k × 2² = 4k

When x = 5

y = k × 5² = 25k

Then

25k - 4k = 20 ( difference between values is 20 )

21k = 20 ( divide both sides by 21 )

k =
`(20)/(21)`

y =
`(20)/(21)` x² ← equation of proportion