1.疑问文[1]中例1研究的是一元三次方程x3-3x-1=0的三个实根的关系,笔者对其解析有一点疑惑,现摘录例1解析中的一段:“所以,原方程的三个根分别在区间(-2,-1)、(-1,1)、(1,2)内.因此,可设x=2cosθ(0<θ<π),则原方程化为8cos3θ-6cosθ-1=0.”用导数研究函数f(x)=x3-3x-1的单调性,并确定根的分布,很容易.问题是:为什么令x= 1. The interrogative text [1] in Example 1 studies the relationship between the three real roots of the unary cubic equation x3-3x-1 = 0. The author has some doubts about the parsing. Therefore, the three roots of the original equation are in the interval (-2,1), (-1,1), (1,2), respectively. Therefore, we can set x = 2 cos θ (0 <θ <π) The equation is 8cos3θ-6cosθ-1 = 0. "It is easy to study the monotonicity of the function f (x) = x3-3x-1 with a derivative and determine the root distribution. The question is: Why x =