(General) This topic examines the nature of functions, the application of derivatives and the relationship between derivatives and monotonicity of functions; (1) If the function is added, it is available to anyone, so it is wrong; ② If the original function is a constant function, it is not monotonous, so it is wrong; 3 correct; (4) if, there are always four? , indicating that the original function is decreasing, so it is wrong; So the correct one is ③;

(real) examine the problem of the maximum value of the function in the open interval and the conditions for the existence of the extreme value, and the extreme value only exists when the derivative function has opposite signs at the left and right points; When,, the original function increases; When, the original function decreases; So, the function takes the minimum value, so?