1. **Problem statement:** Find the point on the curve $y = \sqrt{2x + 1}$ where the normal line is parallel to the line $y = -3x + 6$.
2. **Understanding the problem:** The slope of the given line is $-3$. Since the normal to the curve is parallel to this line, the slope of the normal to the curve must also be $-3$.
3. **Find the slope of the tangent to the curve:**
Given $y = \sqrt{2x + 1} = (2x + 1)^{1/2}$.
Using the chain rule:
$$\frac{dy}{dx} = \frac{1}{2}(2x + 1)^{-1/2} \times 2 = \frac{1}{\sqrt{2x + 1}}$$
4. **Slope of the normal:**
The normal is perpendicular to the tangent, so its slope $m_n$ satisfies:
$$m_n = -\frac{1}{m_t}$$
where $m_t$ is the slope of the tangent.
5. **Set the slope of the normal equal to $-3$:**
$$-\frac{1}{m_t} = -3 \implies m_t = \frac{1}{3}$$
6. **Find $x$ such that $m_t = \frac{1}{3}$:**
$$\frac{1}{\sqrt{2x + 1}} = \frac{1}{3} \implies \sqrt{2x + 1} = 3$$
Square both sides:
$$2x + 1 = 9 \implies 2x = 8 \implies x = 4$$
7. **Find corresponding $y$ value:**
$$y = \sqrt{2(4) + 1} = \sqrt{8 + 1} = \sqrt{9} = 3$$
8. **Answer:** The point is $(4, 3)$.
This corresponds to option (A).
Normal Parallel 02A0Dd
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