(Solved): An inverting OP-AMP with positive feedback has a closed-loop gain of: VinVout=Rf+R ...

An inverting OP-AMP with positive feedback has a closed-loop gain of: $$\frac{V_{\text{out }}}{V_{\text{in }}}=\frac{ARf}{R_f+R_{\text{in }}?A{R}_{\text{in }}}$$ The Laplace expression for $$A$$ is: $$A=\frac{A_0}{\frac{s}{{?}_0}+1}$$ (2) Plug in expression 2 into expression I, get the impulse response, then use the inverse Laplace transform $${\mathcal{L}}^{?1}\left\{\frac{K}{S??}\right\}=K{e}^{?t}$$ to prove that positive feedback is unstable.