验证下列微分方程为全微分方程,并求其解:
(1)(1-4xy)dy=(2y2-3x2)dx;
(2)(3x2y2-4xy)dy+(2xy3-2y2)dx=0;
(3)(x+y2)y'=2x2-y;
(4)xy2dx=(y3-x2y)dy。
A.y=dsolve(y '=x+y+1')
B.y=dsolve('Dy=x+y+1')
C.y=dsolve('Dy=x+y+1'; 'x')
D.y=dsolve('Y'=x+y+1', 'x')
设随机变量(X,Y)的密度函数
试求:(1)系数A;
(2) EX,DX;
(3)EY,DY;
(4)协方差及相关系数。