vector field F = < 2, 3, 5 >
Square S of area 5 is in the plane 2x+y+2z=1 with normal pointing away
from the orgin

find the flux integral
  
 / /
| |   ->    ->
| |   F dot dA
| |
/ /
    S


Answer: the normal to plane is <2,1,2> which does point away from the
orgin. So the unit vector normal to S is <2/3, 1/3, 2/3> so the
flux = 5<2/3, 1/3, 2/3> dot <2, 3, 5> = 5/3(4+3+10) = 85/3