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NDA 2015
Exam
NDA
Year
2015
Subject
Mathematics
Chapter
Quadratic Equation

NDA 2015 · Mathematics · Quadratic Equation

If m and n are the roots of the equation (x+p)(x+q)-k=0 , then the...

If mm and nn are the roots of the equation (x+p)(x+q)−k=0(x+p)(x+q)-k=0, then the roots of the equation (x−m)(x−n)+k=0(x-m)(x-n)+k=0 are

Options

  1. APP and qq
  2. B1p\frac{1}{p} and 1q\frac{1}{q}
  3. C−p-p and −q-q
  4. Dp+qp+q and p−qp-q

Correct answer

C. −p-p and −q-q

Step-by-step solution

Here m and n are the roots of equation. (x+p)(x+q)−k=0x2+x(p+q)+pq−k=0...(i)\begin{aligned} & (x+p)(x+q)-k=0 \\ & x^2+x(p+q)+p q-k=0...(i) \end{aligned} If m and n are the roots of equation, then (x−m)(x−n)=0∴x2−(m+n)x+mn=0...(ii)\begin{array}{ll} & (x-m)(x-n)=0 \\ \therefore \quad & x^2-(m+n) x+m n=0...(ii) \end{array}Now equation (i) should be equal to equation (ii), Now, we have to find roots of (x-m)(x-n)+k=0x2−(m+n)x+mn+k=0x2+(p+q)x+(pq−k)+k=0x2+(p+q)x+pq=0x2+px+qx+pq=0x(x+p)+q(x+p)=0\begin{aligned}& x²-(m+n) x+m n+k=0 \\ & x²+(p+q) x+(p q-k)+k=0 \\ & x²+(p+q) x+p q=0 \\ & x²+p x+q x+p q=0 \\ & x(x+p)+q(x+p)=0 \end{aligned}∴x+q=0 or x+p=0∴x=−q and x=−p∴ Option (C) is correct. \begin{array}{ll}\therefore& x+q=0 \text{ or } x+p=0 \\ \therefore & x=-q\text{ and } x=-p \\ \therefore &\text{ Option (C) is correct. }\end{array}
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