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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: Flaming_Arrow on April 06, 2009, 05:51:46 pm

Title: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 05:51:46 pm
for eg

when i solve it just comes up as
Title: Re: Solving for intersections on the CAS calc
Post by: /0 on April 06, 2009, 06:00:05 pm
Whenever solving fails, graph it and find intersections or use nSolve(
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 06:02:28 pm
whats nSolve?
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 06:37:58 pm
Quote from: pHysiX on April 06, 2009, 06:37:06 pm
u put ur calc in exact mode. change it to approximate

it's on auto
Title: Re: Solving for intersections on the CAS calc
Post by: wombifat on April 06, 2009, 06:55:54 pm
what sort of calculator do you have?
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 07:05:45 pm
ti-89 TIT CAS
Title: Re: Solving for intersections on the CAS calc
Post by: wombifat on April 06, 2009, 07:12:02 pm
ok then no idea :P
Title: Re: Solving for intersections on the CAS calc
Post by: TrueTears on April 06, 2009, 07:39:25 pm
for equations such as , using Solve on the calc will never give you an exact answer even if your calc is in exact mode. To find an approximate answer you must press 'green diamond' + enter to give a decimal answer. Or you can sketch the graph of both and find the intersection, again this will yield an approximate decimal answer.
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 07:43:17 pm
nah i mean when i try solve it they just rearrange the functions, it doesnt give me an exact answer
Title: Re: Solving for intersections on the CAS calc
Post by: TrueTears on April 06, 2009, 07:46:33 pm
Quote from: Flaming_Arrow on April 06, 2009, 07:43:17 pm
nah i mean when i try solve it they just rearrange the functions, it doesnt give me an exact answer
yeah it's impossible to yield an exact answer using solve on the TI-89
Title: Re: Solving for intersections on the CAS calc
Post by: Mao on April 06, 2009, 09:19:05 pm
This is because not all equations have elementary solutions (numbers that cannot be expressed with a finite number of elementary operations). In this case, to yield an approximate, press "Green" + "Enter" to approximate.

Althought sometimes it does that because there isn't a solution. Graphing is the best way to go imo.
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 09:30:33 pm
when i press diamond + enter i get (2.71828)^x-0.5(x+1)=0
Title: Re: Solving for intersections on the CAS calc
Post by: TrueTears on April 06, 2009, 09:53:04 pm
graph it and then use intersection ("F5 -> 5:")
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 06, 2009, 09:54:17 pm
Quote from: TrueTears on April 06, 2009, 09:53:04 pm
graph it and then use intersection ("F5 -> 5:")

yer i know how to do it like that but i was wondering if you could directly to solve it to save time
Title: Re: Solving for intersections on the CAS calc
Post by: TrueTears on April 06, 2009, 09:55:14 pm
for some reason sometimes the calc can not solve some equations. I often graph just to be safe.
Title: Re: Solving for intersections on the CAS calc
Post by: Mao on April 07, 2009, 07:10:36 am
try nSolve
Title: Re: Solving for intersections on the CAS calc
Post by: Flaming_Arrow on April 07, 2009, 11:05:01 am
whats the difference between Solve and nSolve?
Title: Re: Solving for intersections on the CAS calc
Post by: Mao on April 07, 2009, 09:31:25 pm
solve employs algebra (and can give exact solutions), nsolve is simply numeric solving algorithm that uses iteration to get an accurate approximate answer [i.e. many decimals]

solve utilizes nsolve where the expression cannot be solved algebraically, though it does so a LOT slower.