If v = 9i - 5j, find -2 ||v||². Round your answer to the nearest tenth, if necessary. O -20.6 -212 20 6

Calculus: Early Transcendentals
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ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
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**Problem:**

If \( \mathbf{v} = 9\mathbf{i} - 5\mathbf{j} \), find \( -2\|\mathbf{v}\|^2 \). Round your answer to the nearest tenth, if necessary.

**Options:**
- (A) -20.6
- (B) -212
- (C) 20.6
- (D) 212

**Explanation:**

1. First, calculate the magnitude \( \|\mathbf{v}\| \) of the vector \( \mathbf{v} \).

\[
\|\mathbf{v}\| = \sqrt{(9^2) + (-5^2)} = \sqrt{81 + 25} = \sqrt{106}
\]

2. Then, find \( \|\mathbf{v}\|^2 \):

\[
\|\mathbf{v}\|^2 = 106
\]

3. Next, calculate \( -2\|\mathbf{v}\|^2 \):

\[
-2 \|\mathbf{v}\|^2 = -2 \times 106 = -212
\]

The correct answer is \( \boxed{-212} \).
Transcribed Image Text:**Problem:** If \( \mathbf{v} = 9\mathbf{i} - 5\mathbf{j} \), find \( -2\|\mathbf{v}\|^2 \). Round your answer to the nearest tenth, if necessary. **Options:** - (A) -20.6 - (B) -212 - (C) 20.6 - (D) 212 **Explanation:** 1. First, calculate the magnitude \( \|\mathbf{v}\| \) of the vector \( \mathbf{v} \). \[ \|\mathbf{v}\| = \sqrt{(9^2) + (-5^2)} = \sqrt{81 + 25} = \sqrt{106} \] 2. Then, find \( \|\mathbf{v}\|^2 \): \[ \|\mathbf{v}\|^2 = 106 \] 3. Next, calculate \( -2\|\mathbf{v}\|^2 \): \[ -2 \|\mathbf{v}\|^2 = -2 \times 106 = -212 \] The correct answer is \( \boxed{-212} \).
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