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Dhaka Secondary (Higher Secondary) 2011/5

Posted: Fri Jan 28, 2011 10:00 pm
by BdMO
Find the range of the function \[f(x)=\frac{\lceil 2x\rceil-2 \lfloor x \rfloor}{\lfloor 2x \rfloor-2\lceil x\rceil} \]
Here, $\lceil x\rceil$ represents the minimum integer greater than $x$ and $\lfloor x \rfloor$ represents the maximum integer less than $x$.

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Sat Jan 29, 2011 1:12 pm
by Tahmid Hasan
soln for number5(partial)
i came up with only 1 range $-1$.let's express $x$=$p+k$ where p is an integer and k is a fraction.now let's make some cases
csae1. $k=0$.(then x=p).but i find that there is no domain for x as an integer.
case2.$k=\frac{1}{2}$.(i had to do this because of multiplying $x$ by 2)
case3.$0<k<\frac{1}{2}$
case4.$\frac{1}{2}<k<1$
in these cases ,i come up with only 3 solutions,so are they all?

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Sat Jan 29, 2011 2:28 pm
by Zzzz
Please write full solution so that someone can tell whether you are right or wrong or where is your fault...

*to hide something write : [ h i d e ] text [ / h i d e ] (without spaces)

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Sat Jan 29, 2011 4:53 pm
by AntiviruShahriar
Tahmid Hasan wrote:soln for number5(partial)
[\hide]i came up with only 1 range $-1$.let's express $x$=$p+k$ where p is an integer and k is a fraction.now let's make some cases
csae1. $k=0$.(then x=p).but i find that there is no domain for x as an integer.
case2.$k=\frac{1}{2}$.(i had to do this because of multiplying $x$ by 2)
case3.$0<k<\frac{1}{2}$
case4.$\frac{1}{2}<k<1$
in these cases ,i come up with only 1 range $-1$.but i was informed that there are 2 more solutions.[\hide]
for case (¡¡): $(-1)$;
case (¡¡¡): $\frac{-1}{2}$;
case(¡v): $(-2)$...

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Tue Feb 01, 2011 11:28 pm
by Moon
One thing that you must remember here is that the symbols that looks like floors and ceilings are not the same as the usual floors and ceilings! ;)

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Tue Feb 01, 2011 11:31 pm
by Tahmid Hasan
moon bhai eida ki bola lage? :ugeek:

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Tue Feb 01, 2011 11:56 pm
by Moon
ha ha...eita amre confuse kre disilo at first, that's why I posted the caution! :)

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Wed Feb 02, 2011 4:10 pm
by MUjtahid Akon
What about all real numbers 'R' ?

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Wed Feb 02, 2011 4:36 pm
by Avik Roy
actually they were meant to be floors and ceilings, but when it came for describing the unpopular symbols, the words were not exact. that's why the -1 came in the range

Re: Dhaka Secondary (Higher Secondary) 2011/5

Posted: Thu Feb 03, 2011 1:31 am
by Masum
BdMO wrote:Find the range of the function \[f(x)=\frac{\lceil 2x\rceil-2 \lfloor x \rfloor}{\lfloor 2x \rfloor-2\lceil x\rceil} \]
Here, $\lceil x\rceil$ represents the minimum integer greater than $x$ and $\lfloor x \rfloor$ represents the maximum integer less than $x$.
According to the definition if $a$ integer $\lceil a\rceil -\lfloor a\rfloor =2,$otherwise $1$then let $k=\dfrac {\lceil 2x\rceil -2\lfloor x\rfloor} {\lfloor 2x\rfloor -2\lceil x\rceil }$
If $x$ integer $k=1+\frac 6 {\lfloor 2x\rfloor-2\lfloor x\rfloor -4}=-1$
If $x$ not integer,let $x=\lfloor x\rfloor +j $ where $j $ denotes the fractional part of $x,$and then
$k=1+\frac 3 {\lfloor 2x\rfloor -2\lfloor x\rfloor -2}$
Now if $j\le .5,\lfloor 2x\rfloor =\lfloor 2\lfloor x\rfloor \rfloor =2\lfloor x\rfloor ,k=-\frac 1 2$
If $j>.5,\lfloor 2x\rfloor =2\lfloor x\rfloor +1,k=-2$
So $k\in {-1,-2,-\frac 1 2 }$