Derivative Problem

[Bobby Armstrong]

Hello, i need help with this one pronlem,

I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)

f(x) = 1 / (x+1)

The answer i keep getting i know isnt right as you can see or i wouldnt be
asking people on here.

Thanks so much for the time,
Bobby

[David Moran]

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)
f(x) = 1 / (x+1)
The answer i keep getting i know isnt right as you can see or i wouldnt be
asking people on here.
Thanks so much for the time,
Bobby

Show some work so we can check it.

Dave

[Bobby Armstrong]

Well what i have isnt right but this is as far as i got

u need to move everything to the top so: 1(x+1)^-1
and whole numbers = 0 so im at: x^-1
then i mult x*-1 and then take one off of the power
so im at -x^-2 for the derivative
then plug in the x from the point into that and get 0=m
then the y=mx+b
plug in 1=0*0+b so b should = 1
so the equation should be y=0x+1 to by tan to the first graph

im off somewhere and im sure its something easy but i dont see it yet

Post by David Moran

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the
line that crosses tan to point (0,1)
f(x) = 1 / (x+1)
The answer i keep getting i know isnt right as you can see or i wouldnt
be asking people on here.
Thanks so much for the time,
Bobby

Show some work so we can check it.
Dave

[FML]

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)
f(x) = 1 / (x+1)
The answer i keep getting i know isnt right as you can see or i wouldnt be
asking people on here.
Thanks so much for the time,
Bobby

-1/(x+1)^2

[Bobby Armstrong]

How did you get that?

Post by FML

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the
line that crosses tan to point (0,1)
f(x) = 1 / (x+1)
The answer i keep getting i know isnt right as you can see or i wouldnt
be asking people on here.
Thanks so much for the time,
Bobby

-1/(x+1)^2

[Jean-Marc Gulliet]

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)
f(x) = 1 / (x+1)
The answer i keep getting i know isnt right as you can see or i wouldnt be
asking people on here.
Thanks so much for the time,
Bobby

You could use the quotient rule [1], that is
(u/v)' = (v*u' - u*v')/(v^2)

In your case, f(x) = 1/(x + 1), you can write u = 1 and v = (x + 1).
Therefore, we have u' = (1)' = 0 since u is a constant and
v' = (x + 1)'
= (x)' + (1)' -- Addition rule
= 1 + 0
= 1

Thus the derivative of f(x)is going to be

f'(x) = ((x + 1)*0 - 1*1)/(x + 1)^2 = -1/(x + 1)^2

HTH,
Jean-Marc

[1]
http://archives.math.utk.edu/visual.calculus/2/quotient_rule.4/index.html

[The World Wide Wade]

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)
f(x) = 1 / (x+1)

That's pretty much gibberish, and I suspect as long as you pose
problems in this manner, you'll have trouble with them.

[Doc]

I think what he wants here is y=1.

Post by The World Wide Wade

Post by Bobby Armstrong
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)

That's pretty much gibberish, and I suspect as long as you pose
problems in this manner, you'll have trouble with them.

[Frederick Williams]

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)
f(x) = 1 / (x+1)
The answer i keep getting i know isnt right as you can see or i wouldnt be
asking people on here.

The derivative of u^n is nu^{n-1} times the derivative of u, so

f'(x) = -1/(x + 1)^2

and the gradient at (0, 1) has slope

f'(0) = -1.

The eqn of the tangent is therefore

y = (-1)x + c

for some c. Since that line passes through (0, 1)

1 = (-1)0 + c

c = 1.

So the eqn of the tangent at (0, 1) is

y = 1 - x.

[Pubkeybreaker]

Post by Bobby Armstrong
Hello, i need help with this one pronlem,
I need to know the derivative to this equation and the equation to the line
that crosses tan to point (0,1)
f(x) = 1 / (x+1)

It would help if you started by knowing the definition of a derivative.
Generally speaking, one does not compute derivates of an equation.
One computes derivatives of a *function*.

I would also help if you would first learn how to explain what you need

to *yourself*. The phrase "equation to the line that crosses tan "
is meaningless gibberish. What is 'tan'? You you mean the tangent
function? Or do you mean a geometric tangent to f(x)???