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The circuit shown in the figure has an ideal opamp. The oscillation frequency and the condition to sustain the oscillations, respectively, are

1. $\frac{1}{CR}$ and $R_1=R_2 \\$
2. $\frac{1}{CR}$ and $R_1=4R_2 \\$
3. $\frac{1}{2CR}$ and $R_1=R_2 \\$
4. $\frac{1}{2CR}$ and $R_1=4R_2$