can't figure out this simplification

Hello there,

I was asked to do this homework, but first step involves a simplification, We were told a hint: upper path, which contains a couple of resistors won't affect Vo. unfortunately I'm getting stuck at it, I'm unable to see how to prove that path isn't affecting out Voltage in the following circuit

**broken link removed**

thanks mates

If so then why put them in? And if R4 + 2R3 = 0 ohms, then what?

In an ideal op amp circuit, the source impedance of your driving circuit is zero and your output impedance is zero. Therefore your input will produce the voltage it wants to produce, regardless of what it is loaded with. The same for your output voltage. Therefore, looking from the input to the output, your top resistor(s) will have no affect - the source will produce a voltage of Vs. The same for the output - your output will produce a voltage of Vo, regardless of load