# Related Rates

## Homework Statement

Suppose that Y=2((x^2)-3x) and dx/dt = 2
Find dy/dt when x=3

## Homework Equations

the only calc is taking the derivative of the equation, i am wondering if i am doing the whole problem right.

## The Attempt at a Solution

dy/dx = 4x-6
find the equation for x=3 and multiply in 2 for the rate of change of time
Y=4(2*3)-6
Y=18?

I think my answer goes back to the clac. I don't know what number i am supposed to plug in for X, i know it has to do when what X equals at dy/dt and the rate of chage of X over time.

NateTG
Homework Helper
You found
$$\frac{dy}{dx}$$
(The derivative with respect to $x$ when $x=3$.)

$$\frac{dy}{dt}$$
(The derivative with respect to $t$.)

HallsofIvy
Homework Helper

## Homework Statement

Suppose that Y=2((x^2)-3x) and dx/dt = 2
Find dy/dt when x=3

## Homework Equations

the only calc is taking the derivative of the equation, i am wondering if i am doing the whole problem right.

## The Attempt at a Solution

dy/dx = 4x-6
find the equation for x=3 and multiply in 2 for the rate of change of time
Y=4(2*3)-6
Y=18?

I think my answer goes back to the clac. I don't know what number i am supposed to plug in for X, i know it has to do when what X equals at dy/dt and the rate of chage of X over time.

The problem SAYS "Find dy/dt when x= 3"!! What value of x do you think you should put in? The phrase "what x equals at dy/dt" is meaningless.

i understand that 3 must be replaced for x, but where does the dx/dt = 2 fit into the equation? I am guessing around somewhere around the radius portion of the equation