Question
Question 1 (1 point) From the following statements, which one is false? a) \( |x|=\sqrt[3]{x}, x \in R \) b) \( x=\sqrt[3]{x}, x \geq 0 \) c) \( x=\sqrt{x^{2}}, x \geq 0 \) d) \( |x|=\sqrt{x^{2}}, x \in R \)
Ask by Boone Burton. in Canada
Mar 22,2025
Upstudy AI Solution
Tutor-Verified Answer
Answer
Statements (a) and (b) are false.
Solution
**Step 1. Verify Statement (a):**
The statement is
\[
|x|=\sqrt[3]{x} \quad \text{for } x\in \mathbb{R}.
\]
Recall that the cube root function, \(\sqrt[3]{x}\), is defined for all real numbers and is an odd function. This means
\[
\sqrt[3]{x} < 0 \quad \text{if } x < 0,
\]
whereas the absolute value \(|x|\) is always nonnegative.
For a counter‐example, take \(x=-1\):
- Left side: \(|-1| = 1\).
- Right side: \(\sqrt[3]{-1}=-1\).
Since \(1\neq -1\), statement (a) is false.
---
**Step 2. Verify Statement (b):**
The statement is
\[
x=\sqrt[3]{x} \quad \text{for } x\ge0.
\]
For \(x\ge0\) the cube root is defined and is nonnegative, but we must check if the equality holds for every such \(x\).
Test with \(x=8\):
- Left side: \(8\).
- Right side: \(\sqrt[3]{8}=2\).
Since \(8\neq2\), statement (b) does not hold for all \(x\ge0\). Hence, statement (b) is also false.
---
**Step 3. Verify Statement (c):**
The statement is
\[
x=\sqrt{x^2} \quad \text{for } x\ge0.
\]
For any real \(x\), we have the identity
\[
\sqrt{x^2}=|x|.
\]
If \(x\ge0\), then \(|x|=x\). Thus, the equality holds for every \(x\ge0\), and statement (c) is true.
---
**Step 4. Verify Statement (d):**
The statement is
\[
|x|=\sqrt{x^2} \quad \text{for } x\in\mathbb{R}.
\]
As noted, the identity \(\sqrt{x^2}=|x|\) holds true for all real numbers. Therefore, statement (d) is true.
---
**Conclusion:**
The false statements are (a) and (b).
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Extra Insights
The false statement among the options given is: a) \( |x|=\sqrt[3]{x}, x \in R \) This is false because the absolute value function \( |x| \) is not equal to the cube root function \( \sqrt[3]{x} \) for all real numbers \( x \). For example, for \( x = -8 \), \( |x| = 8 \) and \( \sqrt[3]{x} = -2 \). All other statements are true within their specified domains.