Help me finding the current in here please (Circuit analysis)

[FelipeMedLev]

Hi! I've been struggling with this.
Original exercise here: Find the value of Iy when R=0. And the value of Vx when R is infinite.

For the first part of the question I did this since R=0:

I've tried to solve this circuit and I get that Iy and I5 are 0 A, and this can't be possible since Iy is a current source. What am I doing wrong?

The second KVL equation englobes the whole circuit. (Solved the system using Mathematica)

Thanks in advance!

 

[cnh1995]

Your 4th KCL equation is incorrect.
Seeing how you've marked I₂ and I₄, the equation should be I₂=I₄.

 

[FelipeMedLev]

Thanks!

 

[The Electrician]

You should eliminate the 15 ohm resistor in series with the 3Iy current source; resistors in series with ideal current sources have no effect on the rest of the circuit. The only reason to keep it would be if you were required to find the voltage across it, which you are not.

If R=0 there are some things you can determine without solving any equations. If R=0, then Vx=0 and also the 5Vx source equals zero. This means that the voltage across the 8 ohm resistor is zero, and therefore the current I2=0, which means that I4=0 and I3=Iy and I3=I5. You can modify your equations to take these facts into account. You won't need so many equations either.