Understanding KVL and Voltage Differences

[teh_cookie]

Homework Statement

Homework Equations

KVL, the sum of all voltages around a loop equal 0

The Attempt at a Solution

Vx is just the difference of the bottom node to the right node. With KVL I just add up the the voltage differences in a loop and equal to zero right? -15+12+6+Vx=0 Vx = -3 ... However my professor posted the answer and Vx = -9 ... why is that? what am I doing wrong?

 

[anthonuc]

Not sure I never use KCL/KVL anymore lol.

If you know how to use node analysis you can get the answer more quickly and easily.

Establish a node as ground and the voltage at the node you want to solve you just sum the currents into that node to zero.

Establishing the right node as ground:

node analysis equation:

(3-Vx)/3 - 2 = 0

Which solves for Vx = -3

I actually ended up with the same answer as you, perhaps you should ask your professor if it's a typo?

I could've solved it incorrectly as well though.

 

[CEL]

Your solution is correct. Your professor made a mistake.

 

[teh_cookie]

thanks for the help! i just got an email and it was a typo and the answer is -3