设函数u(x,y)=q(x+y)+q(x-y)+定积分(x-y)到(x+y)p(t)dt,其中函数q具有二阶导数,p具有一阶导数,则必有

u(x,y)=q(x+y)+q(x-y)+∫(x-y)到(x+y)p(t)dtu'x=q'(x+y)+q'(x-y)+p(x+y)-p(x-y)u'y=q'(x+y)-q'(x-y)+p(x+y)+p(x-y)u''xx=q''(x+y)+q''(x-y)+p'(x+y)-p'(x-y)u''yy=q''(x+y)+q'’(x-y)+p'(x+y)-p'(x-y)选B.x的二阶偏...