ABCDA1B1C1D1, dx, dy, dz (. 1.5, ), . . , .
A'B'C'D'A1B1C1D1 . 1.5, . D ''CD' (. 1.5, ). u v. + u/x dx, v + v/y dy. AD, dx, , u/x dx, , dy, v/y dy.
.
εx u/x dx dx, . .
εy = dv/dy. , z, εz = dw/dz, w- z.
. 1.6 ABCD . D D' v/x dx, ' ' u/y dy.
γ , . γ = π/2 BAD = BAB + DAD, ' DAD' . , , . .
,
xAz yAz:
:
(3.1)
(3.1) . ( ). , , .