Analysis: (1) Using the assignment method, let y=- 1 be substituted into the abstract function expression to prove the parity of the function;

(2) First, it is proved that f(x) > 0 when x > 0, and then the monotonicity of function f(x) on [0, +∞] is proved by using the definitions of known function and monotone function;

(3) Find the root of f(3)=9 by assignment method, and then solve the inequality by monotonicity of the function.

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I hope this helps.