Continuous Function
1. **State the problem:** We want to find values of $a$ and $b$ such that the piecewise function
$$f(x) = \begin{cases} x^2 + a, & x \geq 3 \\ bx + a, & -3 < x < 3 \\ \sqrt{-b - x}, & x \leq -3 \end{cases}$$
is continuous everywhere.
2. **Continuity conditions:** The function must be continuous at the boundaries $x = -3$ and $x = 3$ where the definition changes.
3. **Continuity at $x=3$:** Left limit (linear) must equal right limit (quadratic) and the function value at $x=3$.
\- From linear side: $\lim_{x\to 3^-} f(x) = 3b + a$
\- From quadratic side: $f(3) = 3^2 + a = 9 + a$
Setting these equal:
$$3b + a = 9 + a \implies 3b = 9 \implies b = 3$$
4. **Continuity at $x = -3$:** Left limit and function value from the square root side equals right limit from the linear side.
\- From square root side (at $x = -3$):
$$f(-3) = \sqrt{-b - (-3)} = \sqrt{-b + 3}$$
\- From linear side (approaching $-3$ from right):
$$\lim_{x \to -3^+} f(x) = b(-3) + a = -3b + a$$
Equate these for continuity:
$$\sqrt{-b + 3} = -3b + a$$
5. **Substitute $b=3$ found from step 3:**
$$\sqrt{-3 + 3} = -3(3) + a \implies \sqrt{0} = -9 + a \implies 0 = -9 + a \implies a = 9$$
6. **Summary:**
$$b=3, \quad a=9$$
These values make the function continuous at $x = -3$ and $x = 3$.
**Final answer:**
$$\boxed{a = 9, \quad b = 3}$$