Calculator doesn't work for this kind of equation?

[kyzoo]

Ok I was doing VCAA 2009 Exam 2, I put the above expression into the calculator as part of my working for the last question...and it comes up with x = -3.1 something??? I had to use trial and error to find x = 240.4. So my question is, why doesn't inputting the above expression into the CAS come up with x = 240.4, even though that is a solution to the equation?

[RainerWolfram]

I think you have to put the domain in.

[kyzoo]

I did, I put x>0, and it comes up with some random algebraically unsolveable equation rather than giving a value of x

[chansthename]

I got that -3.1 answer too, it does tell you more solutions exist though

[kyzoo]

...how r u meant to answer thsi in the exam then? Without trial and error? CSE 2010 Exam 2 has the exact same tpye of question as well....

[cipherpol]

lolz, done this exam yesterday and had the same problem, try putting a domain of 200<x<300

[chansthename]

I did, I put x>0, and it comes up with some random algebraically unsolveable equation rather than giving a value of x

the random algebra is actually the integral with your variable substitued in -1200=0

[kyzoo]

LOL SWEEET ty ty

[chansthename]

lolz, done this exam yesterday and had the same problem, try putting a domain of 200<x<300

did this and it gives me 245.39...

this is not the answer that kyzoo has given. plus how are we supposed to know in an exam what domain to set (I haven't done VCAA 09 yet so if the question had the domain then sorry.)

[kyzoo]

Well u already know a previous part of the question, that if you let x = 180, then the integral ends up being 880ish.

So you can assume that it's bigger than 180.

[InitialDRulz]

idk what they did, but i was looking at some dudes solutions...



EDIT: ok i'm getting -3.1 on my Ti-NSpire...

[98.40_for_sure]

Hahah i remember this question! i spent 20 minutes wondering why it kept coming up with -3 something... then i chucked it into a graph and let it set auto domain/range... tada! CAS is amazing

[jto1292]

I had to CAS trial and error this as well by continually changing the value for t manually until I got 245.397 as a final... Such a time waster. I wonder if VCAA know about this CAS problem :S

[chansthename]

I had to CAS trial and error this as well by continually changing the value for t manually until I got 245.397 as a final... Such a time waster. I wonder if VCAA know about this CAS problem :S

probably why they have that question (ps I was using the classpad and others are using N-spire so it is widespread)

[cameron_15]

I did this more manually, I anti-derived and then just substituted the endpoints into the anti derivate equation function, then told the calculator to solve it. This got me the right answer under exam conditions.

But yes, I had a mini spaz attack when I got a negative distance.