(c) Let $\alpha$ and $\beta$ are the roots then $\alpha + \beta = b,\ \alpha\beta = c$ Given, $|\alpha - \beta| = 1$ $\Rightarrow (\alpha + \beta)^{2} - 4\alpha\beta = 1$ $\Rightarrow b^{2} - 4c = 1$
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Ph.D. in Physics with 19+ years of teaching experience.