49. x2+y2= 1, z= 0 .
. P=y; Q=x; R= 1. ,
, :
50 , L - x2+y2+z2 a2, x+y+z= 0, , Ox.
. , x+y+z= 0, :
- x+y+z= 0, Oz , "+".
, , :
:
51. L - x=a cos t, y=a cos2 t, z=a cos3 t, t.
. t 0 p (x,y,z) L M0(a,a,a) M1(-a,a,-a), t p 2p L , 0. , L L , I =0.
: 0.