# Determine the equation of the tangent line

1. Oct 6, 2012

### Blablablabla

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

$\frac{3x+6}{2-x}$

at $x=3$

2. Relevant equations

y - y$_{o}$ = m(x-x$_{o}$)

3. The attempt at a solution

f(3) = -$\frac{15}{4}$

m = $\frac{3}{0}$ DNE

I have to write the equation in the form of the point-slope formula.

I can get x$_{o}$ and y$_{o}$, but I am having trouble finding m.

Thanks for any help.

2. Oct 6, 2012

### LCKurtz

You didn't give an equation. I suppose it is$$y=\frac{3x+6}{2-x}$$You need to calculate its derivative at $3$ to get the slope. You might also check your $f(3)$.

3. Oct 6, 2012

### Blablablabla

Sorry, yes that is the equation. Can you help me find the derivative? I'm a bit confused because my textbook says that the derivative is

$\frac{f(x+h)-f(x)}{h}$

but in class we learned that as the difference quotient, and that the derivative is when you do this:

y = x$^{n}$
y' = nx$^{n-1}$

That is not the derivative of f(x). You have to take the limit as $h \to 0$ to get the derivative.
That gives the rule for differentiating powers, which is derived from the difference quotient by letting $h\rightarrow 0$. For more complicated derivatives like your quotient, you would use the quotient rule and the power rule. Haven't you had the quotient rule?