().
, , .. .
:
f(x,y,z)=0
f(x,y,z, )=0
, .
.
.
f(x,y,z)=0
.
f(x,y,z,t)=a
.
.
, .
.
δ .
δ(F)=F*δS*cos(F,δS)
+ - .
δ()= + δφ
=0, ( ).
.
, .
.
. .
(F1a, F2a, Fna) .
F1a =-R1; F2a =-R2;..
∑=∑a+∑R=∑FaSk*cos(Fa^;Sk)+
∑RaSk*cos(R^;Sk)=0 .. Fka=-Rk
∑RaSk*cos(R^;Sk)=0
∑a=∑FaSk*cos(Fa^;Sk)=0
∑a=0. =0
( - ).
∑δ+∑δ=0 - -
=0.