设 y =f(x)为可导函数 .①在某个区间内 ,如果 f′(x) 0 ,则 f(x)为增函数 ;如果 f′(x) 0 ,则 f(x)为减函数 .反之亦然 .②函数 f(x)在某点取得极值的充要条件是该点的导数为零且该点两侧的导数异号 .③函数 f(x)在点x0 处的导数 f′(x0 )是曲线y =f(x)在点 (x0 ,f(x0 ) )处 Let y = f(x) be a derivative function. In a certain interval, if f’(x) 0, then f(x) is an increasing function; if f’(x) 0, then f(x) is Decrease the function. And vice versa. 2 The function and value of f(x) at a certain point is that the derivative of this point is zero and the derivative of the two sides of the point is different. The function f(x) is at the point x0. The derivative f′(x0) is the curve y =f(x) at the point (x0,f(x0))