II (x2 + 2 x(y + h)2 + co$x-2(y + h)-(x2 +2 xy2 + cosx-2y))
h-»0 h
lim ń-» o
2x2yh + 2xhz -2 h
/?
lim (4xy + 2x/?-2J = 4xy-2.
t