Find the equation of the midline between the given lines x + 2y − 4 = 0 and x + 2y + 1 = 0
Both lines are parallel because: 1*2 − 2*1 = 0
The slope of the line is: m = − 1/2 = − 0.5
Now we will find the y intercepts values of the lines
The midpoint of this intercepts is a point located on the midline: 

The value of the midpoint (x_{p} , y_{p}) is: (0 , 0.75)
And the midline equation is: y = mx + y_{p} − mx_{p} = − 0.5x + 0.75 + 0.5*0 = − 0.5x + 0.75
And after multiplying all terms by 4 we get the midline equation: 2x + 4y − 3 = 0
