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JEE Advanced 2012Paper 2
Exam
JEE Advanced
Year
2012
Paper
Paper 2
Subject
Mathematics
Chapter
Limits

JEE Advanced 2012 · Paper 2 · Mathematics · Limits

Let α(a) and β(a) be the roots of the equation ( [3] 1+a -1) x^ 2...

Let α(a)\alpha(a) and β(a)\beta(a) be the roots of the equation (1+a3−1)x2+(1+a−1)x+(1+a6−1)=0(\sqrt[3]{1+a}-1) x^{2}+(\sqrt{1+a}-1) x+(\sqrt[6]{1+a}-1)=0 where aa >−1>-1. Then lim⁡a→0+α(a)\lim _{a \rightarrow 0^{+}} \alpha(a) and lim⁡x→0+β(a)\lim _{x \rightarrow 0^{+}} \beta(a) are

Options

  1. A−52-\frac{5}{2} and 1
  2. B−12-\frac{1}{2} and −1-1
  3. C−72-\frac{7}{2} and 2
  4. D−92-\frac{9}{2} and 3

Correct answer

B. −12-\frac{1}{2} and −1-1

Step-by-step solution

(1+a3−1)x2+(1+a−1)x+(1+a6−1)=0(\sqrt[3]{1+a}-1) x^{2}+(\sqrt{1+a}-1) x+(\sqrt[6]{1+a}-1)=0 Let a+1=ya+1=y, then equation reduces to \left(y^{1 / 3}-1\right) x^{2}+(y1/2−1)x+(y1/6−1)=0\left(y^{1 / 2}-1\right) x+\left(y^{1 / 6}-1\right)=0 On dividing both sides by y−1y-1, we get \left(\frac{y^{1 / 3}-1}{y-1}\right) x^{2}+(y1/2−1y−1)x+(y1/6−1y−1)=0\left(\frac{y^{1 / 2}-1}{y-1}\right) x+\left(\frac{y^{1 / 6}-1}{y-1}\right)=0 On taking limit as y→1y \rightarrow 1 i.e. a→0a \rightarrow 0 on both sides, we get 13x2+12x+16=0⇒2x2+3x+1=0⇒x=−1,−12\frac{1}{3} x^{2}+\frac{1}{2} x+\frac{1}{6}=0 \Rightarrow 2 x^{2}+3 x+1=0 \Rightarrow x=-1,-\frac{1}{2} (roots of the equation) ∴lim⁡a→0+α(a)=−1,lim⁡a→0+β(a)=−12\therefore \quad \lim _{a \rightarrow 0^{+}} \alpha(a)=-1, \lim _{a \rightarrow 0^{+}} \beta(a)=-\frac{1}{2}
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