Title: Calculus 4.5
14.5 Linear Approximations, Differentials
and Newtons Method
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3For any function f (x), the tangent is a close
approximation of the function for some small
distance from the tangent point.
4Start with the point/slope equation
linearization of f at a
The linearization is the equation of the tangent
line, and you can use the old formulas if you
like.
5Linearization Example
Find the linear approximation of f(x) x2 at x
1. Use the approximation to 1.12.
6Linearization Example
Find the linear approximation of f(x) x2 at x
1. Use the approximation to 1.12.
7Linearization Example
Use linearization to approximate
8Linearization Example
Use linearization to approximate
9Approximating Binomial Powers
Approximating Binomial Powers this is a special
case of a general linearization formula that
applies to the powers of 1x for small values of
x
Approximating Binomial Powers
10Approximating Binomial Powers
Use this formula to find polynomials that will
approximate the following functions for values of
x close to zero
11Important linearizations for x near zero
This formula also leads to non-linear
approximations
12Differentials
When we first started to talk about derivatives,
we said that becomes when the
change in x and change in y become very small.
dy can be considered a very small change in y.
dx can be considered a very small change in x.
13Let be a differentiable
function. The differential is an
independent variable. The differential is
14Example Consider a circle of radius 10. If the
radius increases by 0.1, approximately how much
will the area change?
very small change in r
very small change in A
(approximate change in area)
15(approximate change in area)
Compare to actual change
New area
Old area
16Newtons Method
Newtons Method numerical method of
approximating the zeros of a function.
17Newtons Method
Finding a root for
We will use Newtons Method to find the root
between 2 and 3.
18Guess
(not drawn to scale)
(new guess)
19Guess
(new guess)
20Guess
(new guess)
21Guess
Amazingly close to zero!
This is Newtons Method of finding roots. It is
an example of an algorithm (a specific set of
computational steps.)
It is sometimes called the Newton-Raphson method
This is a recursive algorithm because a set of
steps are repeated with the previous answer put
in the next repetition. Each repetition is
called an iteration.
22Guess
Amazingly close to zero!
This is Newtons Method of finding roots. It is
an example of an algorithm (a specific set of
computational steps.)
It is sometimes called the Newton-Raphson method
This is a recursive algorithm because a set of
steps are repeated with the previous answer put
in the next repetition. Each repetition is
called an iteration.
23Find where crosses .
24There are some limitations to Newtons method
Looking for this root.
Bad guess.
Wrong root found
Failure to converge
25Newtons method is built in to the Calculus Tools
application on the TI-89.
Of course if you have a TI-89, you could just use
the root finder to answer the problem.
The only reason to use the calculator for
Newtons Method is to help your understanding or
to check your work.
It would not be allowed in a college course, on
the AP exam or on one of my tests.
26Now lets do one on the TI-89
27Now lets do one on the TI-89
Approximate the positive root of
Select and press
.
Calculus Tools
Press (Deriv)
Enter the equation. (You will have to unlock the
alpha mode.)
Set the initial guess to 1.
Set the iterations to 3.
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