Three Methods to Find Roots of Equations

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Three Methods to Find Roots of Equations

There are many different kind of methods which can be used to find the

roots of equations which can not be sold algebraically. In this

coursework we are going to analyse the use of three of these methods

which are called the: change of sign, Newton-Raphson and the

rearrangement method and are going to use them to find roots of

different equations.

Change of sign method

A root of an equation (where the graph crosses the x-axis) can be

detected by finding where the solution of a formula changes sign from

positive to negative. Where we find a change of sign on a graph using

omnigraph we take the range of the numbers it is in and divide it by

ten to find where it now changes sign. This procedure is then repeated

to the required level of accuracy.

Here is a graphical representation of the systematic decimal search:

[IMAGE]

X 1

X 10-1

X10-2

Using change of sign method on excel

First you look up between 2 values (e.g. 1 and 2, or 4 and 5) where

the graph crosses the x-axis. Then you take that as your range and

divide it up into 10 equal segments. For example, if between 1 and 2..

you use 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, etc. you work out the formula

for each of these and where the change of sign occurs you repeat the

process between that range.

A

B

C

D

E

E

1

X1

f(A1)

A2+0.01

f(C1)

C1+0.001

f(C1)

2

A1+0.1

f(A2)

C1+0.01

f(C2)

E1+0.001

f(C2)

3

A2+0.1

f(A3)

C2+0.01

f(C3)

E2+0.001

f(C3)

4

A3+0.1

f(A4)

C3+0.01

f(C4)

E3+0.001

f(C4)

5

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