Find the domain of $\frac{x^2 + 10x + 21}{x^2 + 4x - 21}$.  (Express your answer using interval notation.)
Question:
Find the domain of $\frac{x^2 + 10x + 21}{x^2 + 4x - 21}$.  (Express your answer using interval notation.)
Answer:
Let's think step by step.

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(-\infty, -7)\cup(-7, 3)\cup(3, \infty)
Find the domain of $\frac{x^2 + 10x + 21}{x^2 + 4x - 21}$.  (Express your answer using interval notation.)
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