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1. The input impedance of the non-inverting amp is very high, equal to the input impedance of the op amp input.
The input impedance of a non-inverting amp is equal to the impedance of the network between the input and the inverting op amp terminal (the virtual ground point).
2. The inverting amp can be sum different signals by adding additional input resistors to the summing junction with no interaction between the inputs. Each input is summed independently of the others.
The non-inverting amp can not be used as a summer without interaction between the two inputs. They are not independent.