Let $a, b, c, p, q$ be real numbers. Suppose, $\alpha, \beta$ are the roots of the equation $x^2+2 p x+q=0$…

Let $a, b, c, p, q$ be real numbers. Suppose, $\alpha, \beta$ are the roots of the equation $x^2+2 p x+q=0$ and $\alpha, \frac{1}{\beta}$ are the roots of the equation $a x^2+2 b x+c=0$, where $\beta^2 \notin\{-1,0,1\}$.
Statement $1\left(p^2-q\right)\left(b^2-a c\right) \geq 0$.
Statement $2 b \neq p a$ or $c \neq q a$.
  1. Statement 1 is true, Statement 2 is true, Statement 2 is a correct explanation for Statement 1.
  2. Statement 1 is true, Statement 2 is true, Statement 2 is not a correct explanation for Statement 1.
  3. Statement 1 is true, Statement 2 is false.
  4. Statement 1 is false, Statement 2 is true

Solution

Given, $\alpha$ and $\beta$ are the roots of $x^2+2 p x+q=0$. $ \begin{array}{rlrl} & \therefore & \alpha+\beta & =-2 p \\ \text { and } & \alpha \beta & =q \end{array} $ $\alpha$ and $\frac{1}{\beta}$ are the roots of $a x^2+2 b x+c=0$ and $ \alpha+\frac{1}{\beta}=\frac{-2 b}{a} $ and $ \frac{\alpha}{\beta}=\frac{c}{a} $ $ \text { Now, } \begin{aligned} \left(p^2-q\right)\left(b^2-a c\right) & =\left[\left(\frac{\alpha+\beta}{-2}\right)^2-\alpha \beta\right]\left[\left(\frac{\alpha+\frac{1}{\beta}}{2}\right)^2-\frac{\alpha}{\beta}\right] a^2 \\ & =\frac{(\alpha-\beta)^2}{16}\left(\alpha-\frac{1}{\beta}\right)^2 \cdot a^2 \geq 0 \end{aligned} $ Statement 1 is true. $ \begin{array}{ll} \text { Again now, } & p a=-\left(\frac{\alpha+\beta}{2}\right) a=-\frac{a}{2}(\alpha+\beta) \\ \text { and } & b=-\frac{a}{2}\left(\alpha+\frac{1}{\beta}\right) \\ & p a \neq b \Rightarrow \alpha+\frac{1}{\beta} \neq \alpha+\beta \\ \Rightarrow & \beta \neq 1 \\ \because & \beta^2 \neq\{-1,0,1\}, \text { correct. } \\ \text { Similarly, if } & c \neq q x \\ \Rightarrow & a \frac{\alpha}{\beta} \neq a \alpha \beta \Rightarrow \alpha\left(\beta-\frac{1}{\beta}\right) \neq 0 \end{array} $ $ \begin{array}{ll} \Rightarrow & \alpha \neq 0 \text { and } \beta-\frac{1}{\beta} \neq 0 \\ \Rightarrow & \beta \neq\{-1,0,1\} \end{array} $ Statement 2 is true. Both Statement 1 and Statement 2 are true. But Statement 2 does not explain Statement 1

Asked in: JEE Advanced 2008 (Paper 2)

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