f(x, y) = ln(x - y) - ln(x + y)
f

h = (1, -1)
uxx - uxy - 6uyy = 0
¾ = 3x + y, · = 2x - y.
f(x, y) = x2 + y - ln x3 - 3 ln y
ex-y(cos x - sin x)dx - ex-y cos xdy

ds 1
Å‚(t) = (cos t, sin t, t2) t " [0, 2Ä„]
Å‚ x2+y2+2z 2

y2dx - x2dy Å‚ (0, 0)
Å‚

f(x, y) = x2 - y arcsin y

f h = (1, 2)
3uxx - 5uxy - 2uyy = 0
¾ = 2x + y, · = x - 3y.
f(x, y) = x + y2 - ln y3 - 3 ln x
ex(cosh(x - y) + sinh(x - y))dx - ex sinh(x - y)dy

xyds Å‚(t) = (cos t, sin t, sin t) t " [0, 2Ä„]
Å‚

dy
xdx 1
+ Å‚(t) = (a(t - sin t), a(1 - cos t)) t = Ä„
Å‚ y y-a 6
1
t = Ä„
3