The ideal OP-AMP has the following characteristics.
Ri = `oo`, A = `oo`, R0 = 0
Ri = ``0, A = `oo`, R0 = 0
Ri = `oo`, A = `oo`, R0 = `oo`
Ri = ``0, A = `oo`, R0 = `oo`
Why Ri infinite