方差还有一个性质:若a为常系数,则D(aX)=(a^2)D(X),D(X+a)=D(X)故D(2X-Y)=D(2X)+D(-Y)=(2^2)D(X)+[(-1)^2]D(Y)=4D(X)+D(Y)7.D(X)=36*(1/6)*(1-1/6)=5D(Y)=9*(1/3)*(1-1/3)=2D(X-Y+1)=D(X-Y)=D(X)+D(Y)=5+2=7...