1. Since f(0) = 5 > 0, f(9) < 0, there must be at least one root between 0 and 9.
2. When x approaches negative infinity, f(x) will be negative. This implies that there exists one negative root.
3. When x approaches positive infinity, f(x) will be positive. This means that there is one root greater than 9.
So three real roots. (Sorry in English. If Chinese characters were used, the output was just not right.)