1. **State the problem:** Find the leading coefficient of the polynomial $$f(x) = 10x^2 + 2x - 9x^3$$. 2. **Recall the definition:** The leading coefficient of a polynomial is the coefficient of the term with the highest degree (largest exponent). 3. **Identify the highest degree term:** In $$f(x)$$, the term with the highest power of $$x$$ is $$-9x^3$$ because $$3 > 2 > 1$$. 4. **Extract the leading coefficient:** The coefficient of $$x^3$$ is $$-9$$. 5. **Final answer:** The leading coefficient of $$f(x)$$ is $$\boxed{-9}$$.