Is Every Positive Real Number a Solution to (x+1)(x+2)(x+5)≥36x?

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In summary, the purpose of solving this week's POTW is to exercise problem-solving skills and apply mathematical concepts to real-world scenarios. To solve this week's POTW, the steps include simplifying the equation, setting it equal to 0, finding the roots using the quadratic formula or factoring, and testing values to determine the solution set. To check if your solution is correct, you can plug in the values from the solution set into the original inequality or use a graphing calculator. Some tips for solving this week's POTW include carefully simplifying the equation, using the appropriate formula or method, and practicing similar problems to improve problem-solving skills.
  • #1
anemone
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Here is this week's POTW:

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Prove that every positive real number satisfies $(x+1)(x+2)(x+5)\ge 36x$.

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  • #2
Congratulations to castor28 for his correct solution (Cool) , which you can find below:
We have:
\begin{align*}
(x+1)(x+2)(x+5) - 36x &= x^3 + 8x^2 - 19x + 10\\
&= (x+10)(x-1)^2
\end{align*}
and this is non-negative for all positive $x$ (in fact, for all $x\ge-10$).
 

FAQ: Is Every Positive Real Number a Solution to (x+1)(x+2)(x+5)≥36x?

How do I solve this week's POTW?

To solve this week's POTW, you need to first set the given expression, (x+1)(x+2)(x+5)≥36x, equal to 0. Then, you can use the quadratic formula or factorization to find the roots of the equation. Next, you can plot the roots on a number line and test different intervals to determine the solution set. Finally, you can write the final solution in interval notation.

What is the purpose of setting the expression equal to 0?

Setting the expression equal to 0 allows you to find the roots of the equation, which are the values of x that make the expression equal to 0. These roots are important in determining the intervals to test for the solution set.

How do I use the quadratic formula to solve this POTW?

The quadratic formula is used to find the roots of a quadratic equation in the form ax^2 + bx + c = 0. In this case, the given expression can be rewritten as x^3 + 8x^2 + 17x + 10 = 0. Then, you can plug in the values of a, b, and c into the quadratic formula, x = (-b ± √(b^2 - 4ac)) / 2a, to find the two roots of the equation.

What is factorization and how is it used to solve this POTW?

Factorization is the process of writing an expression as a product of its factors. In this case, the given expression can be factored into (x+1)(x+2)(x+5) = 0. By setting each factor equal to 0, you can find the three roots of the equation. This method is often quicker and easier than using the quadratic formula.

How do I write the final solution in interval notation?

After finding the three roots of the equation, you can plot them on a number line and test different intervals to determine the solution set. The solution set can then be written in interval notation, using parentheses for open intervals and brackets for closed intervals. For example, if the solution set is x ≤ -5 or -2 ≤ x ≤ 2, it can be written as (-∞, -5] ∪ [-2, 2].

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