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Assuming the $\text{OP-AMP}$ to be ideal. the voltage gain of the amplifier shown below is

1. $-\frac{\mathrm{R}_2}{\mathrm{R}_1}$
2. $-\frac{\mathrm{R}_3}{\mathrm{R}_1}$
3. $-\left(\frac{\mathrm{R}_2 \| \mathrm{R}_3}{\mathrm{R}_1}\right)$
4. $-\left(\frac{\mathrm{R}_2+\mathrm{R}_3}{\mathrm{R}_1}\right)$