The largest value of $\dfrac{y}{x}$, where $(x, y)$ is a real number pair satisfying $(x-3)^2 + (y-3)^2 = 6$, is:
Step-by-Step Solution
Key Concept: Maximizing the ratio $y/x$ subject to a circle constraint using the discriminant condition for real intersections
Step 1: Set up the constraint equation by introducing a parameter.
Let $k = \dfrac{y}{x}$, which means $y = kx$. We want to find the maximum value of $k$ for points $(x, y)$ on the circle $(x-3)^2 + (y-3)^2 = 6$.
Substituting $y = kx$ into the circle equation:
$$(x-3)^2 + (kx-3)^2 = 6$$
Step 2: Expand and simplify the equation.
Expanding both squared terms:
$$x^2 - 6x + 9 + k^2x^2 - 6kx + 9 = 6$$
Combining like terms:
$$(1+k^2)x^2 - 6(1+k)x + 12 = 0$$
Step 3: Apply the discriminant condition for real solutions.
For the line $y = kx$ to intersect the circle at real points, the quadratic equation in $x$ must have real solutions. This requires the discriminant to be non-negative:
$$\Delta = [6(1+k)]^2 - 4(1+k^2)(12) \geq 0$$
$$36(1+k)^2 - 48(1+k^2) \geq 0$$
Dividing by 12:
$$3(1+k)^2 - 4(1+k^2) \geq 0$$
Expanding:
$$3(1 + 2k + k^2) - 4(1 + k^2) \geq 0$$
$$3 + 6k + 3k^2 - 4 - 4k^2 \geq 0$$
$$-k^2 + 6k - 1 \geq 0$$
Multiplying by $-1$ (and reversing the inequality):
$$k^2 - 6k + 1 \leq 0$$
Step 4: Solve the quadratic inequality to find the range of $k$.
Using the quadratic formula to find the roots:
$$k = \dfrac{6 \pm \sqrt{36-4}}{2} = \dfrac{6 \pm \sqrt{32}}{2} = \dfrac{6 \pm 4\sqrt{2}}{2} = 3 \pm 2\sqrt{2}$$
Since the coefficient of $k^2$ is positive, the parabola opens upward, so the inequality $k^2 - 6k + 1 \leq 0$ is satisfied between the roots:
$$3 - 2\sqrt{2} \leq k \leq 3 + 2\sqrt{2}$$
Step 5: Identify the maximum value.
The maximum value of $k = \dfrac{y}{x}$ is:
$$k_{\max} = 3 + 2\sqrt{2}$$
**Final Answer:** The largest value of $\dfrac{y}{x}$ is $\boxed{3 + 2\sqrt{2}}$, which corresponds to **Option 3**.
Correct Answer: 4