The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

This discussion is now closed.

Check out other Related discussions

c3 help

hi, i'm resiting c3 in january and i dont know understand chapter 4, numerical methods
i dont get how you can draw the graph (sketch) to find out where the root lies
any help appreciated
Reply 1
Avatar for andiroo
andiroo
Go and buy a graphical calculator. It will sketch the graph for you. The root is where it crosses the x-axis. Some calculators will even give you the root!!!
Reply 2
Avatar for ahezhara
ahezhara
Get the TI-82 Texas Instruments calculator to use in exams.
Reply 3
Avatar for Akido
Akido

you dont need a calc to draw these simple graphs mate, get practising with drawing them, it will help later on.
Reply 4
Avatar for gorilla_baby
gorilla_baby
OP
9
they checked our calc in exams, but the thing is i tried and i just don't know how t osketch them
are we supposed to factorise or something? or is there another way? that's what i need to know how to sketch them,
Reply 5
Avatar for steve2006
steve2006
15
sorry if its OT but u are allowed Gfx calculators in maths exams as long as they cant do symbolic algebra etc. I rung OCR up and they said my gfx calculator the Casio fx-9750 G PLUS is fine to use in the exam.

If worse come to worse get one of these and in 2 button clicks u can get ur root/s
Reply 6
Avatar for qwerty3
qwerty3
6
It is pretty easy to draw the graphs i must say hehe :P and practise always helps just do loads of them and you will get the hang of it
what the hell, you don't understand the basic methods for finding the roots? There are a few different methods: Simple factorisation ala quadratic, decimal search within an interval, linear interpolation, or an iterative method i.e. newton raphson, x = g(x) etc.

Read your text book again and again. There is no way we can tell you how to do the methods on here.
Reply 8
Avatar for qwerty3
qwerty3
6
Horrorshow
what the hell, you don't understand the basic methods for finding the roots? There are a few different methods: Simple factorisation ala quadratic, decimal search within an interval, linear interpolation, or an iterative method i.e. newton raphson, x = g(x) etc.

Read your text book again and again. There is no way we can tell you how to do the methods on here.

ahha no need to be so hard on them haha not everyone is super good at maths although i find it hard to believe sometimes hehe :P
Reply 9
Avatar for JamesD89
JamesD89
Horrorshow
what the hell, you don't understand the basic methods for finding the roots? There are a few different methods: Simple factorisation ala quadratic, decimal search within an interval, linear interpolation, or an iterative method i.e. newton raphson, x = g(x) etc.

Read your text book again and again. There is no way we can tell you how to do the methods on here.


:eek: You're remembering more maths than me, numerical methods was my best chapter in C3, but can't remember having to draw graphs to find roots, only using iteration. Is this a sign of my rustiness or do the exam q's differ a bit for the different boards?
JamesD89
:eek: You're remembering more maths than me, numerical methods was my best chapter in C3, but can't remember having to draw graphs to find roots, only using iteration. Is this a sign of my rustiness or do the exam q's differ a bit for the different boards?


Na I wouldn't worry about it, the boards do differ. Mine, OCR MEI, had a small 18 ums coursework on it so we had to go into some depth. Iteration methods are by far the best and most efficient at converging on the root so don't worry about the others :p:
gorilla_baby
they checked our calc in exams, but the thing is i tried and i just don't know how t osketch them
are we supposed to factorise or something? or is there another way? that's what i need to know how to sketch them,

What are you actually asking? :s-smilie: Factorise what? I mean... what sort of graphs are we talking about here?
Reply 12
Avatar for gorilla_baby
gorilla_baby
OP
9
generalebriety
What are you actually asking? :s-smilie: Factorise what? I mean... what sort of graphs are we talking about here?

cubic graphs, and i do get how to find the roots using these methods you mentioned, it's just that i don't get how to SKETCH the cubic graphs, which is a way of finding the roots by seeing where the graph intercepts the x-axis. I get how to sketch the lnx and e^x graphs and even quadratic ones, but NOT cubic ones...now do you get what i mean?? It's the sketching part, not the using iteration or stuff like that----
gorilla_baby
cubic graphs, and i do get how to find the roots using these methods you mentioned, it's just that i don't get how to SKETCH the cubic graphs, which is a way of finding the roots by seeing where the graph intercepts the x-axis. I get how to sketch the lnx and e^x graphs and even quadratic ones, but NOT cubic ones...now do you get what i mean?? It's the sketching part, not the using iteration or stuff like that----

Well... you probably know already that if the coefficient of x^3 is positive then the curve goes "bottom left" to "top right", and if it's negative then the other way. Other than that, finding any turning points it might have is a good idea. But sketching the curve won't find you the roots...
If you have to draw a cubic in an exam the first thing to do is to use remainder therom to factorise.

Unless its something retarded like x3=yx^3=y

There will normally be a simple root to the cubic like 1 2 -2 or -1 when you have this factor out the (x-2) (x+1) or w/e and then you have a quadratic and a linear factor, factorise the quadratic to get another 2 roots and then you have 3 roots.

These can be plotted on the graph, the general shape is given if it is a −x3-x^3 or a x3x^3 I hope you know what these graphs look like.

+ You should always have the y axis intercept on your graph.

Its like joining the dots with a nice curve after this.

Check the picceh. Its just finding the intercepts and joining the dots...
graphy.JPG7.4KB
Reply 15
Avatar for gorilla_baby
gorilla_baby
OP
9
thomas795135
If you have to draw a cubic in an exam the first thing to do is to use remainder therom to factorise.

Unless its something retarded like x3=yx^3=y

There will normally be a simple root to the cubic like 1 2 -2 or -1 when you have this factor out the (x-2) (x+1) or w/e and then you have a quadratic and a linear factor, factorise the quadratic to get another 2 roots and then you have 3 roots.

These can be plotted on the graph, the general shape is given if it is a −x3-x^3 or a x3x^3 I hope you know what these graphs look like.

+ You should always have the y axis intercept on your graph.

Its like joining the dots with a nice curve after this.

Check the picceh. Its just finding the intercepts and joining the dots...

thanks alot u really helped

Related discussions

Latest

Trending

Trending

Articles for you