So I stumbled across a rather strange ideal op-amp circuit that I've never encountered before. I've done enough problems regarding inverting amplifiers, non-inverting, summing, difference, and such, but I haven't done one that involves two amplifiers together. The problem asked to find both Vo and V4, so I figured that perhaps doing one amplifier at a time would help. Assuming that the voltage difference between the inputs for both inverting and non-inverting terminals was negligible, I framed the left inverting amplifier to include V1, R1, R2, and R3. I attempted at finding the output voltage v_o1, at the end of the left amplifier, through the formula *v_o1 = -(R2/R1)V1, which ended up as -15 V.
However, when attempting to find Vo, I encountered the first roadblock: I know that since the current going into the inverting terminal is zero, i1 = i2 + i3. By using the node-voltage method with this, I identified i2 = (0 - v_o1)/R2 and i3 = (0 -Vo)/R3. This is where I'm unsure if this is all correct. I presumed that the i2 and i3 branches that stemmed off from the node is equal to i1, but could I be wrong about this? I ended up with Vo = 50 V, but I don't fully know whether this is right, or if I'm missing some passive sign somewhere.
As for (b) on finding V4 across the resistor, I think I may had solved this incorrectly. Switching to the second amplifier at the right I assumed that, because we're dealing with ideal amplifiers, the currents from the inverting/non-inverting terminals are zero, such that i4 + i5 = 0. However, considering that Vo might not be correct, I went with my result and ended up with V4 = 90 V. I'm also worried about this because instead of including the whole two amplifiers together, I'm only focusing on one at a time for each part, and that I might very well be missing key variables to include, such as v_o1. Am I wrong in saying this? It would be much appreciated if anyone can provide some insight or advice on this tricky two-stage amplifier circuit. King Regards