Function approaching... something

Calculus Level 3

Let p p be a function where for any positive x x , p ( x ) p(x) is x 7 \frac{x}{7} rounded up to the nearest whole number. Evaluate:

lim n p n ( x ) \lim_{n \to \infty}p^{n}(x)

Where x x and n n are both ANY positive number.

Details and Assumptions

  • p n p^{n} means p p composed n n times, or p ( p ( p ( p ( . . . x ) p(p(p(p(...x)
0 1 1/2 \infty

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1 solution

Finn Hulse
Mar 1, 2014

You can try this with any number. All that this is asking is what value is always approached when you divide by 7, and round up, and divide by 7, etc. If we weren't rounding up, the answer would be 0. If we always rounded down, the answer would also be 0. But everything else is just to look fancy. The problem is just "What happens if you divide by 7 and round up to the nearest whole number infinite times.

Hey buddy is it that p n ( x ) p^{n}(x) is p p being composed n n times? If that is so, you should've mentioned it buddy, I thought that it was raised to the power n n .

Kulkul Chatterjee - 7 years, 3 months ago

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Yeah, I took a guess and luckily my first choice was p p being composed n n times, yeah it should be clarified

Piyal De - 7 years, 3 months ago

No, if you ever see a function raised to a power, it means a function of a function of a funtion n-times.

Finn Hulse - 7 years, 3 months ago

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It can also be such that it's being differentiated n n times.

Piyal De - 7 years, 3 months ago

Finn did you have MathCounts States yesterday? How was it?

Stephen Shamaiengar - 7 years, 3 months ago

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No, it's in 2 weeks. But in advance I will tell you... Not great.;)

Finn Hulse - 7 years, 3 months ago

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What do you mean? :P

Stephen Shamaiengar - 7 years, 3 months ago

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@Stephen Shamaiengar Oh, I'm saying that States is gonna suck. :D

Finn Hulse - 7 years, 3 months ago

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@Finn Hulse Why, because you think a lot of the other people there are going to be better or more prepared? It is true, we experienced the same thing last year.

Stephen Shamaiengar - 7 years, 3 months ago

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@Stephen Shamaiengar Yeah bro, there's Longfellow, Robert Frost, and a couple of other really good schools.

Finn Hulse - 7 years, 3 months ago

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@Finn Hulse Don't forget Thomas Jefferson School for Science and Technology... I think some of those places have a MathCounts class. So they're always really good.

Stephen Shamaiengar - 7 years, 3 months ago

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@Stephen Shamaiengar Oh yeah! I'm kind of scared out of my wits. Wouldn't it be awesome if I made it to Nationals?

Finn Hulse - 7 years, 3 months ago

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@Finn Hulse Yea. I know you're good, but don't get your hopes up. When we went, Stas and Junha from Hornsby did get in the top 15 for the Countdown round but they were literally like 14 and 15 and they were eliminated in the first and second rounds.

Stephen Shamaiengar - 7 years, 3 months ago

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@Stephen Shamaiengar Yeah, exactly.

Finn Hulse - 7 years, 3 months ago

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@Finn Hulse Math Counts sounds really competitive in your states. In Idaho, we basically win every year for state because Idaho stinks. Nobody even tries, except for the schools that have people that throw their kids in a haguan.

Robert Fritz - 7 years, 3 months ago

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@Robert Fritz Oh, it is. VA,TX, CA, and MA are the big 4. They always win.

Finn Hulse - 7 years, 3 months ago

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@Finn Hulse Sounds usual.

Robert Fritz - 7 years, 3 months ago

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@Robert Fritz Maybe I'll see you at Nats!

Finn Hulse - 7 years, 3 months ago

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