Equation Gmatprep

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pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Thu Aug 07, 2008 6:59 am

For how many integers, n is 2^n=n^2 ?
A) 2
B) 3
C) 4
D) 5
E) none

I couldn't find the old post.

I did it by drawing a graph, can someone make it with calculations?

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Source: Beat The GMAT — Problem Solving | Thu Aug 07, 2008 6:59 am

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Thu Aug 07, 2008 7:11 am

i would say A..

only 2 numbers satisfy the equation 2 and 4

2^n=n^2

2^2 = 2^2

4^2 = 2^4..

hope its helps...

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pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Thu Aug 07, 2008 8:25 am

You are right that's 2 but we cannot be totally sure by looking at numbers...
What confused me with my graph was that there is an intersection between the two equations between 0 and -1 but that is not an integer so the answer is 2.
Thanks!

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Xbond: Master | Next Rank: 500 Posts; Posts: 275; Joined: Wed Jul 02, 2008 4:19 am; Thanked: 4 times

by Xbond » Thu Aug 07, 2008 9:42 am

what is OA, please ?

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pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Thu Aug 07, 2008 9:48 am

pepeprepa wrote:You are right that's 2 but we cannot be totally sure by looking at numbers...
What confused me with my graph was that there is an intersection between the two equations between 0 and -1 but that is not an integer so the answer is 2.
Thanks!

Answer is probably 2

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