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They are asking power of 2 in the answer.
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"Powers of 2" is just the title/'nickname' for the question. No way is it related to what the problem statement is.
How can i post questions in this community forum.
This question is from R.D. Sharma - A book of Ninth class in India.
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Is it? I didn't realise (and I've finished that whole book). :P
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Really, that's taught in our school. Definitely that is not even close to Brilliant level 2.
you could also substitute n with 2
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Yes, but that is not a mathematical way to solve.
Relevant wiki: Rules of Exponents
2 n + 1 − 2 n 2 n + 2 n − 1 = 2 n ( 2 ) − 2 n 2 n + 2 2 n = 2 n ( 2 − 1 ) 2 n ( 1 + 2 1 ) = 1 2 3 = 2 3 = 1 . 5 a n s w e r
Yes, the key here is to see that 2 n − 1 = 2 n × 2 − 1 = 2 n × 2 1
Thanks Marvin, your explanation doesn't skip any steps and is clear. Much appreciated :)
By subbing in 1 for n or any number for that matter we will get 3/2
thnx, made it easier:)
Exactly how I solved it!
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Nice! we think alike (:
Such a substition is a good sense check, but it isn't a mathematically acceptable answer ... it doesn't prove the answer is 3/2 for all values of n.
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Which values? Im too lazy to find out myself...
Let 2 n =P
2 P − P P + P / 2
= 2 ( 2 P − P ) 2 P + P
= 4 P − 2 P 2 P + P
= 2 P 3 P
Cut P AND P
= 2 3
Nicely done. By substituting 2^n = P, it makes the expression so much easier to work with...
We know that 2 n + 1 − 2 n = 2 n . Thus 2 n + 1 − 2 n 2 n + 2 n − 1 = 2 n 2 n + 2 n − 1 = 1 + 2 1 = 2 3 = 1 . 5
But the question is what will b the power. of 2 .
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No, the title says that only because powers of 2 are involved. The answer should not be related to the title unless and until strictly specified by the person posting the problem in his/her problem statement.
The correct answer is 1.5 of course, but unusually the problem as posed says n is a <real> number, not the usual <integer>. This shouldn't make any difference, but I guess if you got really sneaky and started mixing up the +ve/-ve sign of sqrt(2) (n=0.5) you could conceivably get something else. By letting n=0.333... you could even make it complex, but you'd be doing some socially unacceptable things with the maths.
Taking any no. in the place of n
You have only shown that the answer is 1.5 for some particular value(s) of n. How do you know that there isn't a value of n that doesn't give the answer of 1.5?
Try with n=1, and you're done... Sure, in that way you cannot be sure the expression is going to simplify "every time" to 3/2, but taking that for granted... This would have been more an interesting question in case the author would have chosen to make an "input a value" type question.
I did make it that. It was changed so it would filter out people who may be under some misconceptions.
Use n=1 as you say and get 2/3, then assume it's true for n=k (some random positive integer), then looking at k+1 we could easily factor out 2 from every term top and bottom and get back to n=k ( you could show the work if you wanted). Therefore, if it's true for some positive integer k, it is also true for k+1. It is calculated to be true for n=1 so it must be true for n=2 and then n=3 ... and so by induction is true for all positive integers n
Take 2 raise to power n common
Yes, I tried that and I got 2 n ( 2 − 1 ) 2 n ( 1 + 2 − 1 )
Common? What do yo mean by that?
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Relevant wiki: Rules of Exponents - Algebraic
This expression can be simplified as
2 n ( 2 1 − 1 ) 2 n ( 1 + 2 − 1 )
= 1 1 + 2 1
= 2 3