In the above activity how do we know that the point lying in 3rd and 8th octant.
The sign convention for various octants are given as:
Octants → | I | II | III | IV | V | VI | VII | VIII |
Coordinates↓ | ||||||||
x | + | − | − | + | + | − | − | + |
y | + | + | − | − | + | + | − | − |
z | + | + | + | + | − | − | − | − |
For 3rd octant, x = -ve, y = -ve and z = +ve
Similarly, for 8th octant, x = +ve, y = -ve and z = -ve
Clearly, on seeing from the given point, the point 
has x and y coordinate negative and z is positive.
Hence, it lies on 3rd octant.
Similarly, on seeing from the given point, the point 
has x coordinate positive and y and z are negative .
Hence, it lies on 8th octant.
Hope you get it!!