66. , =(y+z) + (z+x) +(x+y) , .
. , .. , , rot =0. :
rot = =(11) +(11) +(11) = ,
.
.
1 .
(*), 0 :
2 .
0(0,0,0).
=x +y +z - (x,y,z), N M0; ‑ . N tx, ty, tz.
d = d t. .
(t)=t(y+z) + t(z+x) +t(x+y) .
( (t), )=t(y+z)x+t(z+x)y+t(x+y)z=2t(xy+yz+zx).
, =(xy+yz+zx) = xy+yz+zx.
: xy+yz+zx.
67. , .
: - (L) - , (=0).
, .