# Homework Help: Implicit Differentiation - Tangent Line & Horizontal Tangents

1. Mar 9, 2009

### Pondera

1. The problem statement, all variables and given/known data

Find an equation of the tangent line to this curve at the point (1, -2).

2. Relevant equations

3. The attempt at a solution

2y' = 3x^2+6x
y' = 3x^2+6x
y'=3/2x^2+3x

y+2=3(x-1)
y+2=3x-3
y=3x-5

Last edited: Mar 9, 2009
2. Mar 9, 2009

### lanedance

Hi Pondera

where did the 2 go?
where did the power of x go?
I think the arithmetic needs a little work

3. Mar 9, 2009

### Pondera

Lane, I divided 3x^2+6x by two and got y'=3/2x^2+3x.

By power of x, I take it you mean power of 2? I neglected to put that in here, but it is on my scratch paper, I appologize.

I don't see where the arithmetic is flawed? I certainly believe that that is likely not the equation/form that I need, but I believe I worked what I figured to be correct out correctly. Can you be more specific?

4. Mar 9, 2009

### lanedance

ok I don't really understand what you are trying to do, just picked up some misssing parts as discussed

the question is clipped off when I veiw it

5. Mar 9, 2009

### lanedance

Also the implict derivative w.r.t. x of y2 is not 2y', it will be:

$$\frac{d}{dx} y^2 = 2y \frac{dy}{dx}$$

horizontal derivatives where y' = 0