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March 28, 2024, 10:08:56 pm

Author Topic: "Equation solver" on the ti 89 and 84 question  (Read 2867 times)  Share 

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rowshan

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"Equation solver" on the ti 89 and 84 question
« on: October 28, 2008, 04:57:58 pm »
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what answer does your calc give to this:
cos(a) + .2sin(a) = .9975
Mine gives -.6951

It is set in degree mode.
The correct answer is 23.3 degrees
GAH!

This is the last step of last question of the kilbaha 08 spec 2 exam. 
I'm wondering why it isn't working! Anyone got any ideas?

/0

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #1 on: October 28, 2008, 05:35:24 pm »
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That's odd, mine gives 23.3 (TI-89)
Are you sure your syntax is correct?

BiG DaN

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #2 on: October 28, 2008, 05:42:47 pm »
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what answer does your calc give to this:
cos(a) + .2sin(a) = .9975
Mine gives -.6951

It is set in degree mode.
The correct answer is 23.3 degrees
GAH!

This is the last step of last question of the kilbaha 08 spec 2 exam. 
I'm wondering why it isn't working! Anyone got any ideas?

my ti-84 does same as u :S
2008 - Methods (36), Further (44), Physics (34)
2009 - English Language (37), Chem (29), Specialist (27), P.E. (42)
Enter - 94.85

dekoyl

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #3 on: October 28, 2008, 05:43:47 pm »
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The solver on Ti-84 only gives one solution.
If you graph it, you'll see that there is a solution at 23.3.

(I don't do spec. but I think this is what you want.)

rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #4 on: October 28, 2008, 05:55:17 pm »
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umm
nSolve(cos(x)+.2sin(x)=.9975,x)

shinny

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #5 on: October 28, 2008, 05:56:33 pm »
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OK THIS IS WEIRD. I was getting the right answer, and after mucking around a bit, now it gives me the one you're getting. I'll muck around a bit longer and see what causes it to change...
MBBS (hons) - Monash University

YR11 '07: Biology 49
YR12 '08: Chemistry 47; Spesh 41; Methods 49; Business Management 50; English 43

ENTER: 99.70


rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #6 on: October 28, 2008, 05:58:07 pm »
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oh and on my 84, i just switch shove it all in the equation solver, 0 = -.9975+ cos(x) + .2sin(x)

and i get -.6975 =S

rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #7 on: October 28, 2008, 05:58:50 pm »
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SPOOOOOOKY WOOOOOOO

shinny

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #8 on: October 28, 2008, 06:16:05 pm »
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Oh, its just because they're both viable solutions and I got lucky the first time that the calc didn't notice the negative one. I assume the question came with a domain restriction, and you have to key that into the bound section to ensure that you get the 23.3 answer. Either that, or if you know roughly what figure you want (i.e. a number in between 0 and 90 degrees), type something like 45 into the x= section first as a guess, and then solve it and the calc will choose the closest value.
MBBS (hons) - Monash University

YR11 '07: Biology 49
YR12 '08: Chemistry 47; Spesh 41; Methods 49; Business Management 50; English 43

ENTER: 99.70


rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #9 on: October 28, 2008, 06:19:16 pm »
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1) you got lucky? Calc didn't notice?
2) where do i key in this bound?
3) it didn't really come with a bound but you can infer that its between 0 and 90.

rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #10 on: October 28, 2008, 06:21:04 pm »
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Oh there is a bound thingy on the 84, but when i put in 0-90 it says bad guess. Where do i put it in for the 89?

shinny

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #11 on: October 28, 2008, 06:35:03 pm »
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After you key in the bound, you have to change your guess (which is where the X= is, change that number to around 45 before hitting alpha enter) to prevent BAD GUESS from coming up. As for the 89, you can add a domain restriction by adding '|x>0 and x<90' (exactly as I've typed it there) after your solve command.
MBBS (hons) - Monash University

YR11 '07: Biology 49
YR12 '08: Chemistry 47; Spesh 41; Methods 49; Business Management 50; English 43

ENTER: 99.70


rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #12 on: October 28, 2008, 06:49:16 pm »
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cheers buddy!!!

rowshan

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #13 on: October 28, 2008, 06:54:52 pm »
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no working on the ti 89 though
i have typed in the stuff in the square brackets exactly
[solve(cos(x)+.2sin(x)=.9975,x) '|x>0 and x<90' ]
it comes up as syntax error. =(

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Re: "Equation solver" on the ti 89 and 84 question
« Reply #14 on: October 28, 2008, 06:55:47 pm »
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no working on the ti 89 though
i have typed in the stuff in the square brackets exactly
[solve(cos(x)+.2sin(x)=.9975,x) '|x>0 and x<90' ]
it comes up as syntax error. =(

What are the quotation marks for? You don't need them