解决函数零点存在问题常使用函数零点存在定理:函数y=f(x)在区间[a,b]上的图象是一条不间断的曲线,且f(a)f(b)<0,则函数y=f(x)在区间(a,b)上有零点.但这个定理的逆命题是不成立的,即函数y=f(x)在开区间(a,b)上有零点,则f(a)f(b)<0不一定成立,所以定理中的条件仅是函数f(x)在(a,b)上有零点的充分条件,而不是充要条件. To solve the problem of the zero point of the function, the existence theorem of zero point is always used: the function y = f (x) is an uninterrupted curve in the interval [a, b] The function y = f (x) has zeros in the interval (a, b), but the inverse of this theorem is not valid, ie the function y = f (x) has zeros in the interval (a, b) (a) f (b) <0 does not necessarily hold, so the condition in the theorem is only the sufficient condition for the function f (x) to have zero on (a, b), not the necessary and sufficient condition.