coordinate geometry

given point doesnt satisfy the line means we have equation of a diagonal and one of the vertex which does not lie on the given diagonal,

we know that diagonals of square intersects at 90o.

so equation of other diagonal 2x+y = c it passes through (1,4) => c=6

i.e. equation of other diagonal 2x+y = 6

now we can find the length of perpendicular from (1,4) on x-2y+2=0 it will be a/2 where a is the side of the square.

now find the line which makes 45o angle from x-2y+2=0 and passes through (1,4)

this will give you one side of the square.

the other through this point will be perpendicular to first one which can also be found.

the other two sides will be parallel to these sides and length of perpendicular on these sides will be equal to 'a'

which we have found earlier.

so you can get the equations of all the sides.