中原大學九十三學年度碩士班入學招生考試
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科目:工程數學  
1. (20%) Consider two independent random variables which are both Gaussian (or normal) distributed with zero mean and variance . Determine the probability density function of .
 
2. (15%) Let A be an n*m matrix with m>n and 0 denote the n*1 all-zero vector. Consider a set H consisting of all the m*1 vectors x satisfying Ax=0. Suppose we have Az=w for some constant vectors z and w. Please show that x is a solution of Ax=w if and only if x=z+u for some uH.
   
3.
(20%) Consider a continuous random variable X.X is said to be memoryless if Pr{X>t+h|X>t}=Pr{X>h} for constants h and t . Please show that X is memoryless if and only if X is exponentially distributed.
   
4.
(20%) Let V=,where x denotes the variable and R is the set consisting of all real numbers. Define the inner product of functions f(x)and g(x)
 
  Please show that V forms a vector basis over R , and find an orthonormal basis for V.
 
5. (15%) Consider a random variable X and a discrete random variable Z with the probability mass function:Pr{z=+1}=Pr{z=-1}=1/8 and Pr{z=+2}=Pr{z=-2}=3/8, which is independent of X. Let Y=XY.
  (7%)(a) Are X and Y uncorrelated? Why?
 
(8%)(b) Are X and Y independent? Why?
   
6. (10%) Consider a set V consisting of all piecewise continuous functions with period 2L, i.e.,V forms a vector space over the field consisting of all complex numbers, and is a basis for V, where Z+ denotes the set containing all positive integers. Please show that also forms a basis for V, where Z stands for the set containing all integers.
     
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