Prove Inequality: $m,n,k\in N$, $m>1,n>1$

In summary, an inequality is a comparison between two quantities. When m, n, and k are in the set of natural numbers, it means they are positive integers including zero. When m and n are greater than 1, it means they are larger than the number 1. To prove an inequality, mathematical properties and operations are used to show one side is greater than the other. For example, if m > 1 and n > 1, then m + n > m can be proven by adding 1 to both sides, subtracting m, and showing 1 > n is true.
  • #1
Albert1
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$m,n,k\in N$, and $m>1,n>1$
prove :
$(3^{m+1}-1)\times (5^{n+1}-1)\times(7^{k+1}-1)>98\times 3^m\times 5^n\times7^k$
 
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  • #2
becauase m > 1and n > 1
$(3^{m+1}-1)\times (5^{n+1}-1)\times(7^{k+1}-1)$
= $3^m(3- \frac{1}{3^m})\times 5^n(5-\frac{1}{5^n})\times 7^k(7- \frac{1}{7^k})$
= $3^m\times 5^n \times 7^k (3- \frac{1}{3^m})(5-\frac{1}{5^n})(7- \frac{1}{7^k})$
$\ge \ 3^m\times 5^n \times 7^k (3- \frac{1}{3^2})(5-\frac{1}{5^2})(7- \frac{1}{7})$ putting minimum values of m,n,k
$\ge 98.25 \times 3^m\times 5^n \times 7^k$ (used a calculator)
$\gt 98 \times 3^m\times 5^n \times 7^k$
 
  • #3
kaliprasad said:
becauase m > 1and n > 1
$(3^{m+1}-1)\times (5^{n+1}-1)\times(7^{k+1}-1)$
= $3^m(3- \frac{1}{3^m})\times 5^n(5-\frac{1}{5^n})\times 7^k(7- \frac{1}{7^k})$
= $3^m\times 5^n \times 7^k (3- \frac{1}{3^m})(5-\frac{1}{5^n})(7- \frac{1}{7^k})$
$\ge \ 3^m\times 5^n \times 7^k (3- \frac{1}{3^2})(5-\frac{1}{5^2})(7- \frac{1}{7})$ putting minimum values of m,n,k
$\ge 98.25 \times 3^m\times 5^n \times 7^k$ (used a calculator)
$\gt 98 \times 3^m\times 5^n \times 7^k$
nice solution!
 

FAQ: Prove Inequality: $m,n,k\in N$, $m>1,n>1$

What is an inequality?

An inequality is a mathematical statement that compares two quantities, indicating that one is greater than, less than, or equal to the other.

What does it mean for m, n, and k to be in the set of natural numbers?

When m, n, and k are in the set of natural numbers, it means that they are positive integers (whole numbers) including zero.

What does it mean for m and n to be greater than 1?

When m and n are greater than 1, it means that they are both larger than the number 1. This also implies that they are positive integers.

How do you prove an inequality?

To prove an inequality, you must use mathematical properties and operations to manipulate the given quantities and show that one side is greater than the other.

Can you give an example of proving an inequality with natural numbers?

Yes, for example, we can prove that for any natural numbers m and n, if m > 1 and n > 1, then m + n > m. We can start by adding 1 to both sides of the inequality, giving us m + 1 > m + n. Then, we can subtract m from both sides, leaving us with 1 > n. Since n is a natural number and we know that 1 is the smallest natural number, this statement is true. Therefore, we have proven the inequality.

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