Q3(a) WTF!!!! (1 Viewer)

[thunderdax]

OK, who else was confused with question 3 a (ii)? Halving the interval gives 0.8, but if you halve the interval again then it becomes obvious that 0.7 is a closer approximation than 0.8... Is this the right way to do it or should I have just said 0.8?

 

[queenie]

it said once.. i think i just left it at 0.8

 

[stv_87]

i think i said 0.7 because it said to one decimal place so u cant use 0.75 and then 0.7 is better than 0.8. i was bewildred initially but 0.7 is correct though i did not study that cause face it that was three gift marks. if wrong then so many people would have done 0.7 ie 99% of state and the other one percent would have just instinctively used newton, cause thats what it usually is.

 

[EvilDude]

Didn't say once. Just said use the method. After 2 it was closer to 0.7, I said 0.7

 

[thunderdax]

Now I'm feeling better about it. Thanks for that. Halving the interval is such a crappy technique because of this.

 

[who_loves_maths]

Originally Posted by EvilDude
Didn't say once. Just said use the method. After 2 it was closer to 0.7, I said 0.7

that question was horrifically worded. they should, in theory, accept both 0.7 or 0.8 as the right answer.

yes sure the question didn't say used the method ONCE. BUT, it also didn't mention anything about a BETTER or CLOSER approximation either!
so any approximation (within reason) should be acceptable, otherwise the question can be construed as misleading.

also, the word "approximation" means exactly that - an approximation. so since the question didn't mention a "better" or "closer" approximation, then that's no reason to discriminate one approximation over the other. as long as one showed the working for halving the interval, then x = 0.8 should be quite a reasonable approximation in theory.

 

[reggina_calcio]

that question was horrifically worded. they should, in theory, accept both 0.7 or 0.8 as the right answer.

yes sure the question didn't say used the method ONCE. BUT, it also didn't mention anything about a BETTER or CLOSER approximation either!
so any approximation (within reason) should be acceptable, otherwise the question can be construed as misleading.

also, the word "approximation" means exactly that - an approximation. so since the question didn't mention a "better" or "closer" approximation, then that's no reason to discriminate one approximation over the other. as long as one showed the working for halving the interval, then x = 0.8 should be quite a reasonable approximation in theory.

You put 0.8 didnt you?






So did I!

 

[MarsBarz]

I halved it once. I hope that was correct. I agree that the question was somewhat ambiguous.

 

[who_loves_maths]

Originally Posted by reggina_calcio
You put 0.8 didnt you?

So did I!

^ hehe... that's a no-brainer

but honestly, i'm not just saying what i did to "defend" myself... i actually consciously thought of all that during the exam whilst trying to make up my mind to put either 0.7 or 0.8

my thinking was that, since 1) the question gave a 0.7 as an approximation already, and 2) that otherwise there's not reason to discriminate between both, than i put x=0.8 down thinking that it was a "safer" answer.

also, after 2 halving procedures - you would arrive at x = 0.75 . let's say you decide to stop there (which is reasonable since f(0.75) = 0.003, yet the next iteration gives f(0.725) = -0.02 or something which is not closer than x=0.75 would give), then you would have to round up answer to 2 dec. pl.
i.e. 0.75 ---> 0.8 !

 

[_dhj_]

Since it asks for 1 dec place, you're supposed to give a solution correct to one decimal place. The root was between 0.7 and 0.75 (not inclusive, as neither values give you f(x)=0) after the 2nd approximation, which means it must be 0.7 "to one decimal place" as anything less than 0.75, e.g. 0.74999 would have to be rounded down.

 

[who_loves_maths]

^ well, like i said, the question was ambiguous. so "what you're supposed to do" - is a subjective notion. it depends on the interpretation of the question.
so in any case, i believe x = 0.8 should be acceptable for the examiners.

 

[Huratio]

it said once.. i think i just left it at 0.8

i did this as well..
it didn't specify the number of approximations that you had to do. im thinking 0.8 is the right answer.

 

[tofu]

im thinking because it was 2 marks 1 mark for 0.8 but full marks for 0.7

 

[jake2.0]

well my teacher says that 0.7 is the right answer as you have to keep repeating the process untill the second decimal stops changing

 

[lfc_reds2003]

WLM, howd u find it

and howd u find 4u

im sure u did well bud

 

[richz]

WLM, is gonna top mx1 and mx2 this year, i'll put my money on that

 

[wanton-wonton]

The root is between 0.725 and 0.75, so to one decimal place, it must be 0.7.

 

[word.]

this is what you do
the root is approx 7.5 x 10^-1 to 1 d.p.

 

[haboozin]

yea what wanton-wonton did was right..

you half it then half it again (to check your answer)

and its def 0.7...
it was actually in an old hsc where they did the same thing and people got tricked with the same thing....

this is what this yrs's maths was all about - help put off people, so only the best shine.

 

[Abtari]

the question said use the method of halving the interval to find AN approximation...

this doesnt' neccessarily mean an approximation with one try of the halving interval or with two tries or with three tries or whatever...

because this is not specified, both answers are acceptable.

correct to one decimal place is the most stupid thing i have ever heard for a question like that, which has a root between 0.7 and 0.9... wtf

and, yeah, as for myself, i did it once, got 0.75 and thought nothing of doing it twice, so put o.8 as my answer to 1 d.p.

but seriously, that question is a joke, and noone should fret about whether it is 0.7 or 0.8. The only reason I put 0.8 and did it once was cos it just didn't seem right to put 0.7 as an approximation to a root "between" 0.7 and 0.9