Question

If the value of "y" varies directly with "x"

and y = -1 when x = 3, find "y" if x = 9.
Enter the number that belongs in the green box.
y = [?]

Answer 1

y = - 3

Explanation:

Given that y varies directly with x then the equation relating them is

y = kx ← k is the constant of variation

To find k use the condition y = - 1 when x = 3, then

k =
`(y)/(x)` = -
`(1)/(3)`, thus

y = -
`(1)/(3)` x ← is the equation of variation

When x = 9, then

y = -
`(1)/(3)` × 9 = - 3