1.
2.
3.
4. f(x;y)≥0, . f(x;y)≥ φ(x;y),
5. . .
6. f(x;y) D, . S, , m M . . . - D.
7. f(x;y) D, . S, - Ǝ . (x0;y0), . f(x0;y0) = - f(x;y) - D.
.
, f(x;y)≥0, . D. , z = f(x;y). . . , S(x) -, ﬩ Ox, a b - -, . . D , . Oy, . . . f(x;y)≥0.
.
x = r cos φ, y = r sin φ, dxdy = rdrdφ.
φ.