What is the **domain** of the real-valued function $g(x) = x^{3} + \sqrt{x + 2} - 10$?
AAll real numbers
BAll real numbers $x$ such that $x \ge -2$
CAll real numbers except $-2$
DAll real numbers $x$ such that $x \ge 2$
Answer & Solution
Correct answer: B. All real numbers $x$ such that $x \ge -2$
The domain of a real-valued function is the set of inputs for which the output is a real number. Examine each piece of $g(x) = x^{3} + \sqrt{x + 2} - 10$:
- $x^{3}$ is defined for all real $x$.
- $\sqrt{x + 2}$ is real **only when** the radicand is non-negative: $x + 2 \ge 0$, i.e. $x \ge -2$.
- $-10$ is a constant.
The overall function is defined wherever **every** piece is defined. The binding constraint is the square root: $x \ge -2$.
- Trap A ignores the square-root restriction.
- Trap B treats $\sqrt{x+2}$ as if it were $1/(x+2)$ — i.e. excludes a single point rather than a half-line.
- Trap D solves $x - 2 \ge 0$ instead of $x + 2 \ge 0$ (sign error inside the radical).
The domain is $\{x \in \mathbb{R} : x \ge -2\}$, or in interval notation $[-2, \infty)$.
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