These are some problems taken from the book 'Practical Electronics for Inventors (3rd Ed)'
I'm wondering what I'm doing wrong as I get different answers for the ones marked in red
b) Vac = 12v - 9v = 3v
Vbd = 0v - 0v = 0v
Vad = 12v - 0v = 12v
Vbc = 0v - 9v = -9v ????
c) Vac = 12v - 0v = 12v
Vbd = 0v - (-9v) = 9v ????
Vad = 12v - (-9v) = 21v ????
Vbc = 0v - 0v = 0v
I'm wondering what I'm doing wrong as I get different answers for the ones marked in red
b) Vac = 12v - 9v = 3v
Vbd = 0v - 0v = 0v
Vad = 12v - 0v = 12v
Vbc = 0v - 9v = -9v ????
c) Vac = 12v - 0v = 12v
Vbd = 0v - (-9v) = 9v ????
Vad = 12v - (-9v) = 21v ????
Vbc = 0v - 0v = 0v