Given that $a, b$ and $c$ are real numbers such that $b^2=4 a c$ and $a>\gamma_0$. The maximal possible set…

Given that $a, b$ and $c$ are real numbers such that $b^2=4 a c$ and $a>\gamma_0$. The maximal possible set $D \subseteq R$ on which the function $f: D \rightarrow R$ given by $f(x)=\log \left\{a x^3+(a+b) x^2+(b+c) x+c\right\}$ is defined, is
  1. $R-\left\{-\frac{b}{2 a}\right\}$
  2. $R-\left(\left\{-\frac{b}{2 a}\right\} \cup(-\infty,-1)\right)$
  3. $R-\left(\left\{-\frac{b}{2 a}\right\} \cup\{x: x \geq 1\}\right)$
  4. $R-(\{-b / 2 a\} \cup(-\infty,-1])$

Solution

Given function, $ \begin{gathered} f(x)=\log \left\{a x^3+(a+b) x^2+(b+c) x+c\right\} \\ =\log \left\{\left(a x^2+b x+c\right)(x+1)\right\} \end{gathered} $ The function $f(x)$ will be define, if $ \begin{aligned} & \Rightarrow \quad\left(a x^2+b x+c\right)(x+1)>0 \\ & \text { and } \\ & x+1>0 \quad\left\{\because a>0 \text { and } b^2=4 a c\right\} \\ & \end{aligned} $ So, $\left\{D=x: x \in(-1, \infty)\right.$ and $\left.x \neq-\frac{b}{2 a}\right\}$ or $ D=R-\left\{-\frac{b}{2 a}\right\} \cup(-\infty,-1] . $

Asked in: AP EAMCET 2018 (22 Apr Shift 1)

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