Quotient remainder theorem problem.

In summary, by plugging in $4q+r$ for $n$ in the expression $n(n^2-1)(n+2)$, we get the product of four consecutive integers, which will always be divisible by 4. This can be proven using the Quotient Remainder Theorem, which states that any integer can be written as $4q+r$ where $0\le r<4$. Therefore, for any integer $n$, $4|n(n^2-1)(n+2)$.
  • #1
tmt1
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For any int $$n $$ , prove that $$ 4 | n (n^2 - 1) (n + 2)$$.

I know I have to use the quotient remainder theorem, but I'm wondering how to go about this problem.

I'm not sure how to phrase this problem in English.
 
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  • #2
Couple of hints.

1. $n(n^2-1)(n+2)=(n-1)\, n \,(n+1)(n+2)$.
2. By the Quotient Remainder Theorem, there exist integers $q$ and $r$ such that $n=4q+r$, where $0\le r<4$.

Does this suggest anything to you?
 
  • #3
Ackbach said:
Couple of hints.

1. $n(n^2-1)(n+2)=(n-1)\, n \,(n+1)(n+2)$.
2. By the Quotient Remainder Theorem, there exist integers $q$ and $r$ such that $n=4q+r$, where $0\le r<4$.

Does this suggest anything to you?

Right, so $(n-1)\, n \,(n+1)(n+2)$ is 4 consecutive integers. I get that if you take any arbitrary integer, if it is not divisible by 4, you can increment it by some int $c$ such that $0< c < 4$ and get an int that is divisible by 4.

Therefore, if you have 4 consecutive integers, one of those integers will be divisible by 4, and as a result the product of those 4 integers will be divisible by 4. I just don't know how to state or prove this formally.
 
  • #4
tmt said:
Right, so $(n-1)\, n \,(n+1)(n+2)$ is 4 consecutive integers. I get that if you take any arbitrary integer, if it is not divisible by 4, you can increment it by some int $c$ such that $0< c < 4$ and get an int that is divisible by 4.

Therefore, if you have 4 consecutive integers, one of those integers will be divisible by 4, and as a result the product of those 4 integers will be divisible by 4. I just don't know how to state or prove this formally.

Why not plug in $4q+r$ in for $n$, and see what comes out in the wash?
 

FAQ: Quotient remainder theorem problem.

What is the Quotient Remainder Theorem?

The Quotient Remainder Theorem is a mathematical principle that states that when dividing one integer by another, the result can be expressed as a quotient and a remainder. For example, when dividing 13 by 5, the quotient is 2 and the remainder is 3.

How is the Quotient Remainder Theorem used in problem-solving?

The Quotient Remainder Theorem is often used in problem-solving to simplify large division problems. Instead of having to perform a long division, the theorem allows us to quickly determine the quotient and remainder without the need for extra calculations.

Can the Quotient Remainder Theorem be used for any type of division?

This theorem can only be used for division of integers, meaning whole numbers that can be positive, negative, or zero. It cannot be applied to division involving decimals or fractions.

What is the difference between a quotient and a remainder?

A quotient is the result of division, while a remainder is the amount left over after dividing. In other words, the quotient tells us how many times the divisor can fit into the dividend evenly, while the remainder is the leftover amount that cannot be divided evenly.

Can the Quotient Remainder Theorem be applied to more than two numbers?

Yes, the Quotient Remainder Theorem can be applied to any number of integers. For example, if we want to divide 50 by 6, the quotient is 8 with a remainder of 2. We can then take that remainder of 2 and continue dividing it by another integer to get another quotient and remainder.

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