ATAR Notes: Forum
VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Specialist Mathematics => Topic started by: rowshan 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?
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That's odd, mine gives 23.3 (TI-89)
Are you sure your syntax is correct?
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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
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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.)
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umm
nSolve(cos(x)+.2sin(x)=.9975,x)
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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...
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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
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SPOOOOOOKY WOOOOOOO
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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.
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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.
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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?
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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.
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cheers buddy!!!
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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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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
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Ah crap, I didn't mean exactly as I've typed it there as in with the quotation marks ahah
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oooo right lol...awesome thanks!
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the numerical solve function is rather "incomplete". this is the case with the equation solver on 84, and the nSolve function [as well as solve function on 89 when it doesn't have an exact solution]
what it does is it searches from left to right, and return the first matching approximate value then disregard everything else. that's why on the 89 when you ask it to solve a rather complex thing, it always says "warning: more solutions may exist" in the bottom left.