Question

Suppose y varies directly with x. if y=-3 when x=5 find y when x=-1

Answer 1

The value of y at x=-1 is 3/5.

Explanation:

It is given that y varies directly with x. It means y is directly proportional to x.

`y\propto x`

`y=kx` .... (1)

where, k is constant of proportionality.

It is given that y=-3 when x=5.

Substitute y=-3 and x=5 in equation (1).

`-3=k(5)`

`-(3)/(5)=k`

The value of k is -3/5.

`y=-(3)/(5)x` .... (2)

We need to find the value of y when x=-1.

Substitute x=-1 in equation (2).

`y=-(3)/(5)(-1)`

`y=(3)/(5)`

Therefore the value of y at x=-1 is 3/5.

Answer 2

solve for "k", to find the "constant of variation",
then plug it back in the y = kx, to get the equation
now
what's is y when x = -1?
well, just plug that in the equation with the found "k" value,
to get "y" :)