Gradient Zero
1. Stating the problem: We want to find the x-coordinate of the point on the curve $y = (x + 2)\sqrt{1 - 2x}$ where the gradient (derivative) is zero.
2. Express the function: Let $y = (x + 2)\sqrt{1 - 2x}$.
3. Rewrite $y$ to facilitate differentiation: Note that $\sqrt{1 - 2x} = (1 - 2x)^{\frac{1}{2}}$, so
$$y = (x+2)(1 - 2x)^{\frac{1}{2}}.$$
4. Use the product rule to find $\frac{dy}{dx}$: If $y = u v$ with
$$u = x+2 \quad \text{and} \quad v = (1-2x)^{\frac{1}{2}},$$
then
$$\frac{dy}{dx} = u'v + uv'.$$
5. Compute the derivatives:
$$u' = \frac{d}{dx}(x+2) = 1,$$
$$v' = \frac{d}{dx}(1-2x)^{\frac{1}{2}} = \frac{1}{2}(1-2x)^{-\frac{1}{2}} \cdot (-2) = -\frac{1}{(1-2x)^{\frac{1}{2}}}.$$
6. Substitute back:
$$\frac{dy}{dx} = 1 \cdot (1-2x)^{\frac{1}{2}} + (x+2) \cdot \left(-\frac{1}{(1-2x)^{\frac{1}{2}}}\right) = (1-2x)^{\frac{1}{2}} - \frac{x+2}{(1-2x)^{\frac{1}{2}}}.$$
7. Combine into a single fraction:
$$\frac{dy}{dx} = \frac{(1-2x) - (x+2)}{(1-2x)^{\frac{1}{2}}} = \frac{1 - 2x - x - 2}{(1-2x)^{\frac{1}{2}}} = \frac{-3x - 1}{(1-2x)^{\frac{1}{2}}}.$$
8. Set the gradient equal to zero:
$$\frac{dy}{dx} = 0 \implies \frac{-3x - 1}{(1-2x)^{\frac{1}{2}}} = 0.$$
Since the denominator cannot be zero (domain restriction: $1-2x > 0 \Rightarrow x < \frac{1}{2}$), the numerator must be zero:
$$-3x -1 = 0 \, \Rightarrow \, 3x = -1 \, \Rightarrow \, x = -\frac{1}{3}.$$
9. Check the domain: $x = -\frac{1}{3} < \frac{1}{2}$, so valid.
**Final answer:** The x-coordinate where the gradient is zero is
$$x = -\frac{1}{3}.$$