# A Bijection

For two sets $X=\{x \mid -1 \leq x \leq 1\}, Y=\{y \mid 9 \leq y \leq 11\},$ a bijective function $$f: X \to Y$$ is defined as $$f(x)=ax+b,$$ where $$a > 0.$$ What is $$ab?$$

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