- The document discusses three circuit analysis problems involving operational amplifiers. - For the first circuit, it is shown that the current flowing into node A equals zero using Kirchhoff's current law. - For the second circuit, it is shown that the voltage at node 3 equals zero by applying Kirchhoff's voltage law at nodes 1 and 2. This allows expressing the input voltage in terms of the output voltage. - For the third circuit, Kirchhoff's laws are again applied at two nodes to eliminate the voltage at one node and express the input voltage in terms of the output voltage.