# Slopes of Tangents and Secants 2

• February 12th 2009, 04:44 PM
Dickson
Slopes of Tangents and Secants 2
Sorry I'm pretty sure it said post a new thread for a different question....well here it is:

lim f(a + h) - f(a) / h
h->0

Use that forumla to find the slope of the tangent line of the cubic funciotn y = x^3 at the point (1,1)

This formula keeps messing me up.
• February 12th 2009, 04:48 PM
Jhevon
Quote:

Originally Posted by Dickson
Sorry I'm pretty sure it said post a new thread for a different question....well here it is:

lim f(a + h) - f(a) / h
h->0

Use that forumla to find the slope of the tangent line of the cubic funciotn y = x^3 at the point (1,1)

This formula keeps messing me up.

you want $f'(1) = \lim_{h \to 0} \frac {f(1 + h) - f(1)}h$

where $f(x) = x^3$

what is $f(1)$, $f(1 + h)$?
• February 12th 2009, 04:49 PM
skeeter
$f(x) = x^3$

$a = 1$

$f(1+h) = (1+h)^3 = 1 + 3h + 3h^2 + h^3$

$f(1) = 1$

now find the limit of the difference quotient.
• February 12th 2009, 04:52 PM
Dickson
Yeah see I used sum of cubes for the top