a1= 1 b1=2 a2=2 b2=4
Here is where I get confused I understand that they must get a dz in the equations thus they take the derivative with respect to y of the following equation z=x+2y
thus giving dz=dx+2 or dz-dx/2
What I dont understand is the simplification process that occurs now
then the book goes on to transform it into
7dx + (2z-1)dz=0
I have no idea what they did to get to that step.