Question

Find an equation of variation where y varies jointly as x and the square of z, and where y=70, when x=21 and z=5.

Answer 1

`y = 181.75xz^2`

Explanation:

Given

y jointly varies to x and z^2

Required

Find the equation

We start by writing out the variation;

`y\ \alpha\ xz^2`

Write as equation

`y = kxz^2`

Substitute values of x,y and z

`70 = k * 21 * 25^2`

`70 = k * 21 * 25 * 25`

`70 = k * 13125`

Divide both sides by 7

`(70)/(13125) = (k * 131251)/(13125)`

`(70)/(13125) = k`

`187.5 = k`

`k = 181.75`

Substitute k in
`y = kxz^2`

`y = 181.75xz^2`