a 1 aπ 3a 3 =A Γ = A π = = 1 ∴A A 3 =2 2 2 42 aπ 33 ∴XE=
4 2aa3
π ∫+ ∞0+∞
0xe3
x 22a
xd
2= π∫4
e tdt= t
2aπx a22
(Γ) 2=2a
π
QXE =3 a
π∫+
0∞xe
4
dx= 22aπ
∫
∞+
0t et dt 32
23 a 2a2 25 2 a 1 3 π = =Γ = 2 π 2 2 π
3a 2 4a2 4 2 2 23 2 a = ∴D X= XE E X=2 π 2 π 19