We can follow the simple rule as –
- Note the coefficients of the objective.
- If both are negative, draw the objective line in the 3rd quadrant
- If coefficient of x1 is (-)ve but that of the x2 is (+)ve, draw it is 2nd quadrant
- If coefficient of x1 is (+)ve but that of the x2 is (-)ve, draw it is 4th quadrant
- If both are positive, draw the objective line in the 1st quadrant
- Then move the objective line towards the origin – that’s the direction
(a)
z = 4×1 – 2×2; The coefficient of x1 is (+)ve but that of the x2 is (-)ve, so, draw it is 4th quadrant and move towards the origin.

(b)
z = -3×1 + x2; The coefficient of x1 is (-)ve but that of the x2 is (+)ve, so, draw it is 2nd quadrant and move towards the origin.

(c)
z = -x1 – 2×2, Here, both the coefficients are negative so, draw the objective line in the 3rd quadrant.
