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JEE Main 201219 MayOnline
Exam
JEE Main
Year
2012
Date
19 May
Mode
Online
Subject
Mathematics
Chapter
Quadratic Equation

JEE Main 2012 · 19 May · Online · Mathematics · Quadratic Equation

Consider a quadratic equation a x^2+b x+c=0 , where 2 a+3 b+6 c=0...

Consider a quadratic equation ax2+bx+c=0a x^2+b x+c=0, where 2a+3b+6c=02 a+3 b+6 c=0 and let g(x)=ax33+bx22+cxg(x)=a \frac{x^3}{3}+b \frac{x^2}{2}+c x. Statement 1: The quadratic equation has at least one root in the interval (0,1)(0,1). Statement 2: The Rolle's theorem is applicable to function g(x)g(x) on the interval [0,1][0,1].

Options

  1. AStatement 1 is false, Statement 2 is true.
  2. BStatement 1 is true, Statement 2 is false.
  3. CStatement 1 is true, Statement 2 is true, Statement 2 is not a correct explanation for Statement 1.
  4. DStatement 1 is true, Statement 2 is true, , Statement 2 is a correct explanation for Statement 1.

Correct answer

D. Statement 1 is true, Statement 2 is true, , Statement 2 is a correct explanation for Statement 1.

Step-by-step solution

Let g(x)=ax33+b⋅x22+cxg(x)=\frac{a x^3}{3}+b \cdot \frac{x^2}{2}+c x \mathrmg^{\prime}(x)=a x²+b x+c Given: ax2+bx+c=0and2a+3b+6c=0a x^2+b x+c=0 and 2 a+3 b+6 c=0 Statement-2: (i) g(0)=0 and g(1)g(1)=a3+b2+c=2a+3b+6c6=06=0⇒g(0)=g(1)\begin{aligned}& =\frac{a}{3}+\frac{b}{2}+c=\frac{2 a+3 b+6 c}{6}\\ & =\frac{0}{6}=0 \\ & \Rightarrow g(0)=g(1) \end{aligned}(ii)(ii)giscontinuousonis continuous on[0,1] and differentiable on (0,1)∴(0,1)\therefore By Rolle's theorem ∃k∈(0,1)\exists k \in(0,1) such that g′(k)=0g^{\prime}(k)=0 This holds the statement 2. Also, from statement-2, we can say ax2+bx+c=0a x^2+b x+c=0 has at least one root in (0,1)(0,1). Thus statement-1 and 2 both are true and statement-2 is a correct explanation for statement-1.
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