CONCEPT: Perpendicular distance of a plane ax+by+cz+d=0 from a point P(x1,y1,z1) is given by: d=|‌
ax1+by1+cz1+d
√a2+b2+c2
| CALCULATION: Let A(x,y,z) be the foot of the perpendicular drawn fromthe origin to the plane x+y+z=3. As we know that, the perpendicular distance of a plane ax+by+cz+d=0 from a point P(x1,y1,z1) is given by: d=|‌
ax1+by1+cz1+d
√a2+b2+c2
| So, the distance betweenthe origin and the plane x+y+z−3=0 is given by: d=|‌
0+0+0−3
√12+12+12
|=‌
3
√3
=√3 So, this means that the length of the line joining the points origin and A is √3 As we can see that from the given options, if A=(1,1,1)then the distance between the points origin and A is √3 Hence, correct option is 3 .