厦门淘宝美工培训学费:不对f(x)=(x-1)(x-2)(x-3)(x-4)求导,求f'(X)=0的实根,并指出区间

来源:百度文库 编辑:神马品牌网 时间:2024/05/03 19:50:42

(x-1)(x-2)(x-3)(x-4)
= [(x - 1)(x - 4)]*[(x - 2)(x - 3)]
= (x^2 - 5x + 4)*(x^2 - 5x + 6)
= (x^2 - 5x + 5)^2 - 1

令 u = x^2 - 5x + 5 则有

f(x) = u^2 - 1
f'(x) = 0 的实数根肯定在 f(u) 的顶点处,有:
u = 0

x^2 - 5x + 5 = 0
x1 = (5 + √5)/2
x2 = (5 - √5)/2

用导数的定义做

好像我们也在学这个哦,不过我数学一点都不好啦