Example Question - geometric mean

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Calculating Specific Expansion Terms and Investigating Geometric Mean Relation

For the 2nd question (problem 8), since it is cut off, we are unable to provide a complete solution. However, for the 3rd question (problem 9), we can proceed: <p>The sum of the two numbers is $6$ times their geometric mean, then </p> <p>Let the two numbers be $a$ and $b$. Given that $a+b = 6\sqrt{ab}$ and we are to show that $a$ and $b$ are in the ratio $(3 + 2\sqrt{2}):(3 - 2\sqrt{2})$.</p> <p>Since we have a ratio of sums to a geometric mean, let's assume $a = (3 + 2\sqrt{2})k$ and $b = (3 - 2\sqrt{2})k$, where $k$ is some positive constant.</p> <p>\[ a + b = (3 + 2\sqrt{2})k + (3 - 2\sqrt{2})k\]</p> <p>\[ a + b = 3k + 2\sqrt{2}k + 3k - 2\sqrt{2}k\]</p> <p>\[ a + b = 6k\]</p> <p>The geometric mean of $a$ and $b$ is $\sqrt{ab}$:</p> <p>\[\sqrt{ab} = \sqrt{(3 + 2\sqrt{2})k \cdot (3 - 2\sqrt{2})k}\]</p> <p>\[\sqrt{ab} = \sqrt{(9 - 8)k^2}\]</p> <p>\[\sqrt{ab} = k\]</p> <p>Now, we compare the sum and geometric mean:</p> <p>\[6k = 6\sqrt{ab}\]</p> <p>\[k = \sqrt{ab}\]</p> <p>This confirms that the sum of $a$ and $b$ is indeed $6$ times their geometric mean, and thus the numbers are in the desired ratio.</p> For question 9, which discusses mean and standard deviation, no specific mathematical equations are shown, and thus a solution cannot be provided based on the information given in the image.

Comparing Arithmetic and Geometric Mean for Positive Numbers

这个问题是关于算术平均数和几何平均数的比较的。根据题意,算术平均数为80,几何平均数是某个正数的平方,要求我们找出这个正数的可能值。 假设这个正数为x,因为几何平均数是x的平方,所以我们有: 算术平均数 = (x + x²) / 2 = 80 这是一个二次方程,我们可以将其改写为: x² + x - 160 = 0 我们使用求根公式(负b加减根号下b平方减4ac除以2a),得: x = [-1 ± √(1 + 4 * 160)] / 2 接下来,我们来计算: x = [-1 ± √641] / 2 显然,因为求的是正数的可能值,我们只需考虑带正号的解: x = [-1 + √641] / 2 ≈ (25.2 - 1) / 2 ≈ 24.2 / 2 ≈ 12.1 所以符合题目条件的正数x的大致值是12.1。然而,查看选项,我们看到最接近的整数值是11,所以最恰当的选项是 (A) 11。

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