题目设随机变量X的概率密度为 varphi(x)=Ae^-(|x|)/(2) ,则A=( )。A. 2B. 1C. (1)/(2)D. (1)/(4)设随机变量X的概率密度为 $\varphi(x)=Ae^{-\frac{|x|}{2}}$ ,则A=( )。A. 2B. 1C. $\frac{1}{2}$D. $\frac{1}{4}$题目解答答案D. $\frac{1}{4}$