<< Chapter < Page Chapter >> Page >

Key concepts

  • Newton’s method approximates roots of f ( x ) = 0 by starting with an initial approximation x 0 , then uses tangent lines to the graph of f to create a sequence of approximations x 1 , x 2 , x 3 ,… .
  • Typically, Newton’s method is an efficient method for finding a particular root. In certain cases, Newton’s method fails to work because the list of numbers x 0 , x 1 , x 2 ,… does not approach a finite value or it approaches a value other than the root sought.
  • Any process in which a list of numbers x 0 , x 1 , x 2 ,… is generated by defining an initial number x 0 and defining the subsequent numbers by the equation x n = F ( x n 1 ) for some function F is an iterative process. Newton’s method is an example of an iterative process, where the function F ( x ) = x [ f ( x ) f ( x ) ] for a given function f .

For the following exercises, write Newton’s formula as x n + 1 = F ( x n ) for solving f ( x ) = 0 .

f ( x ) = x 3 + 2 x + 1

F ( x n ) = x n x n 3 + 2 x n + 1 3 x n 2 + 2

Got questions? Get instant answers now!

f ( x ) = e x

F ( x n ) = x n e x n e x n

Got questions? Get instant answers now!

For the following exercises, solve f ( x ) = 0 using the iteration x n + 1 = x n c f ( x n ) , which differs slightly from Newton’s method. Find a c that works and a c that fails to converge, with the exception of c = 0 .

f ( x ) = x 2 4 , with x 0 = 0

| c | > 0.5 fails, | c | 0.5 works

Got questions? Get instant answers now!

f ( x ) = x 2 4 x + 3 , with x 0 = 2

Got questions? Get instant answers now!

What is the value of c for Newton’s method?

c = 1 f ( x n )

Got questions? Get instant answers now!

For the following exercises, start at

a. x 0 = 0.6 and

b. x 0 = 2 .

Compute x 1 and x 2 using the specified iterative method.

x n + 1 = 2 x n ( 1 x n )

a. x 1 = 12 25 , x 2 = 312 625 ; b. x 1 = −4 , x 2 = −40

Got questions? Get instant answers now!

x n + 1 = 1 x n

a. x 1 = 1.291 , x 2 = 0.8801 ; b. x 1 = 0.7071 , x 2 = 1.189

Got questions? Get instant answers now!

x n + 1 = 3 x n ( 1 x n )

Got questions? Get instant answers now!

x n + 1 = x n 2 + x n 2

a. x 1 = 26 25 , x 2 = 1224 625 ; b. x 1 = 4 , x 2 = 18

Got questions? Get instant answers now!

x n + 1 = | x n |

a. x 1 = 6 10 , x 2 = 6 10 ; b. x 1 = 2 , x 2 = 2

Got questions? Get instant answers now!

For the following exercises, solve to four decimal places using Newton’s method and a computer or calculator. Choose any initial guess x 0 that is not the exact root.

x 4 100 = 0

3.1623 or 3.1623

Got questions? Get instant answers now!

x 3 x = 0

0 , −1 or 1

Got questions? Get instant answers now!

x + tan ( x ) = 0 , choose x 0 ( π 2 , π 2 )

0

Got questions? Get instant answers now!

1 + x + x 2 + x 3 + x 4 = 2

0.5188 or 1.2906

Got questions? Get instant answers now!

x 3 + ( x + 1 ) 3 = 10 3

Got questions? Get instant answers now!

For the following exercises, use Newton’s method to find the fixed points of the function where f ( x ) = x ; round to three decimals.

tan ( x ) on x = ( π 2 , 3 π 2 )

4.493

Got questions? Get instant answers now!

ln ( x ) + 2

0.159 , 3.146

Got questions? Get instant answers now!

Newton’s method can be used to find maxima and minima of functions in addition to the roots. In this case apply Newton’s method to the derivative function f ( x ) to find its roots, instead of the original function. For the following exercises, consider the formulation of the method.

To find candidates for maxima and minima, we need to find the critical points f ( x ) = 0 . Show that to solve for the critical points of a function f ( x ) , Newton’s method is given by x n + 1 = x n f ( x n ) f ( x n ) .

Got questions? Get instant answers now!

What additional restrictions are necessary on the function f ?

We need f to be twice continuously differentiable.

Got questions? Get instant answers now!

For the following exercises, use Newton’s method to find the location of the local minima and/or maxima of the following functions; round to three decimals.

Minimum of f ( x ) = x 2 + 2 x + 4

Got questions? Get instant answers now!

Minimum of f ( x ) = 3 x 3 + 2 x 2 16

x = 0

Got questions? Get instant answers now!

Minimum of f ( x ) = x 2 e x

Got questions? Get instant answers now!

Maximum of f ( x ) = x + 1 x

x = −1

Got questions? Get instant answers now!

Maximum of f ( x ) = x 3 + 10 x 2 + 15 x 2

Got questions? Get instant answers now!

Maximum of f ( x ) = x x 3 x

x = 5.619

Got questions? Get instant answers now!

Minimum of f ( x ) = x 2 sin x , closest non-zero minimum to x = 0

Got questions? Get instant answers now!

Minimum of f ( x ) = x 4 + x 3 + 3 x 2 + 12 x + 6

x = −1.326

Got questions? Get instant answers now!

For the following exercises, use the specified method to solve the equation. If it does not work, explain why it does not work.

Newton’s method, x 2 + 2 = 0

Got questions? Get instant answers now!

Newton’s method, 0 = e x

There is no solution to the equation.

Got questions? Get instant answers now!

Newton’s method, 0 = 1 + x 2 starting at x 0 = 0

Got questions? Get instant answers now!

Solving x n + 1 = x n 3 starting at x 0 = −1

It enters a cycle.

Got questions? Get instant answers now!

For the following exercises, use the secant method , an alternative iterative method to Newton’s method. The formula is given by

x n = x n 1 f ( x n 1 ) x n 1 x n 2 f ( x n 1 ) f ( x n 2 ) .

Find a root to 0 = x 2 x 3 accurate to three decimal places.

Got questions? Get instant answers now!

Find a root to 0 = sin x + 3 x accurate to four decimal places.

0

Got questions? Get instant answers now!

Find a root to 0 = e x 2 accurate to four decimal places.

Got questions? Get instant answers now!

Find a root to ln ( x + 2 ) = 1 2 accurate to four decimal places.

−0.3513

Got questions? Get instant answers now!

Why would you use the secant method over Newton’s method? What are the necessary restrictions on f ?

Got questions? Get instant answers now!

For the following exercises, use both Newton’s method and the secant method to calculate a root for the following equations. Use a calculator or computer to calculate how many iterations of each are needed to reach within three decimal places of the exact answer. For the secant method, use the first guess from Newton’s method.

f ( x ) = x 2 + 2 x + 1 , x 0 = 1

Newton: 11 iterations, secant: 16 iterations

Got questions? Get instant answers now!

f ( x ) = sin x , x 0 = 1

Newton: three iterations, secant: six iterations

Got questions? Get instant answers now!

f ( x ) = e x 1 , x 0 = 2

Got questions? Get instant answers now!

f ( x ) = x 3 + 2 x + 4 , x 0 = 0

Newton: five iterations, secant: eight iterations

Got questions? Get instant answers now!

In the following exercises, consider Kepler’s equation regarding planetary orbits, M = E ε sin ( E ) , where M is the mean anomaly, E is eccentric anomaly, and ε measures eccentricity.

Use Newton’s method to solve for the eccentric anomaly E when the mean anomaly M = π 3 and the eccentricity of the orbit ε = 0.25 ; round to three decimals.

Got questions? Get instant answers now!

Use Newton’s method to solve for the eccentric anomaly E when the mean anomaly M = 3 π 2 and the eccentricity of the orbit ε = 0.8 ; round to three decimals.

E = 4.071

Got questions? Get instant answers now!

The following two exercises consider a bank investment. The initial investment is $ 10,000 . After 25 years, the investment has tripled to $ 30,000 .

Use Newton’s method to determine the interest rate if the interest was compounded annually.

Got questions? Get instant answers now!

Use Newton’s method to determine the interest rate if the interest was compounded continuously.

4 . 394 %

Got questions? Get instant answers now!

The cost for printing a book can be given by the equation C ( x ) = 1000 + 12 x + ( 1 2 ) x 2 / 3 . Use Newton’s method to find the break-even point if the printer sells each book for $ 2 0 .

Got questions? Get instant answers now!

Questions & Answers

what is microbiology
Agebe Reply
What is a cell
Odelana Reply
what is cell
Mohammed
how does Neisseria cause meningitis
Nyibol Reply
what is microbiologist
Muhammad Reply
what is errata
Muhammad
is the branch of biology that deals with the study of microorganisms.
Ntefuni Reply
What is microbiology
Mercy Reply
studies of microbes
Louisiaste
when we takee the specimen which lumbar,spin,
Ziyad Reply
How bacteria create energy to survive?
Muhamad Reply
Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments
_Adnan
But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?
Muhamad
they make spores
Louisiaste
what is sporadic nd endemic, epidemic
Aminu Reply
the significance of food webs for disease transmission
Abreham
food webs brings about an infection as an individual depends on number of diseased foods or carriers dully.
Mark
explain assimilatory nitrate reduction
Esinniobiwa Reply
Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).
Elkana
This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products
Elkana
Examples of thermophilic organisms
Shu Reply
Give Examples of thermophilic organisms
Shu
advantages of normal Flora to the host
Micheal Reply
Prevent foreign microbes to the host
Abubakar
they provide healthier benefits to their hosts
ayesha
They are friends to host only when Host immune system is strong and become enemies when the host immune system is weakened . very bad relationship!
Mark
what is cell
faisal Reply
cell is the smallest unit of life
Fauziya
cell is the smallest unit of life
Akanni
ok
Innocent
cell is the structural and functional unit of life
Hasan
is the fundamental units of Life
Musa
what are emergency diseases
Micheal Reply
There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️
_Adnan
define infection ,prevention and control
Innocent
I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life
Lubega
Heyy Lubega hussein where are u from?
_Adnan
en français
Adama
which site have a normal flora
ESTHER Reply
Many sites of the body have it Skin Nasal cavity Oral cavity Gastro intestinal tract
Safaa
skin
Asiina
skin,Oral,Nasal,GIt
Sadik
How can Commensal can Bacteria change into pathogen?
Sadik
How can Commensal Bacteria change into pathogen?
Sadik
all
Tesfaye
by fussion
Asiina
what are the advantages of normal Flora to the host
Micheal
what are the ways of control and prevention of nosocomial infection in the hospital
Micheal
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 2

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Calculus volume 1. OpenStax CNX. Feb 05, 2016 Download for free at http://cnx.org/content/col11964/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Calculus volume 1' conversation and receive update notifications?

Ask