In the theorem for judging the existence of zero, if f (a) f (b) >: 0 has the possibility of zero besides zero, the number of zero is even. This proposal holds.

Judge the number of zeros:

1. Just take the derivative of the function, judge the monotonous interval from the positive and negative of the derivative function, and divide (a, b) into several monotonous intervals;

2. In every monotone interval, the existence of zero is judged by the existence judgment theorem of zero. (Each monotone interval has at most one zero, that is, the number of zeros can only be 0 or1);

3. Add the zeros in each monotonous interval to get the zeros in (a, b) interval.