If α, β are the roots of the equation x^2 – px + q = 0, then the quadratic equation whose roots are α/β and α/β is ……………………
If α, β are the roots of the equation x2 – px + q = 0, then the quadratic equation whose roots are α/β and α/β is ……………………
A) qx2 + (2q – p2 ) x + q = 0
B) q2x – px + 1 = 0
C) qx2 + (p2 – 2q) x + q = 0
D) qx2 – px – 1 = 0
2 Answers
Correct option is (A) qx2 + (2q – p2)x + q = 0
Given that \(\alpha\;\&\;\beta\) are roots of equation \(x^2-px+q=0.\)
\(\therefore\) Sum of roots \(=\frac{-(-p)}1=p\)
\(\Rightarrow\) \(\alpha+\beta\) = p ______________(1)
& Product of roots \(=\frac q1=q\)
\(\Rightarrow\) \(\alpha\beta=q\) ______________(2)
Now, \(\frac{\alpha}{\beta}+\frac{\beta}{\alpha}\) \(=\frac{\alpha^2+\beta^2}{\alpha\beta}\)
\(=\frac{(\alpha+\beta)^2-2\alpha\beta}{\alpha\beta}\)
\(\Rightarrow\) \(\frac{\alpha}{\beta}+\frac{\beta}{\alpha}\) \(=\frac{p^2-2q}q\) ______________(3) (From (1) & (2))
And \(\frac{\alpha}{\beta}.\frac{\beta}{\alpha}\) \(=\frac{\alpha\beta}{\alpha\beta}\) = 1 ______________(4)
\(\therefore\) Quadratic equation whose roots are \(\frac{\alpha}{\beta}\;and\;\frac{\beta}{\alpha}\) is
\(x^2-(\frac{\alpha}{\beta}+\frac{\beta}{\alpha})x+\frac{\alpha}{\beta}.\frac{\beta}{\alpha}=0\)
\(\Rightarrow x^2-(\frac{p^2-2q}q)x+1=0\) (From (3) & (4))
\(\Rightarrow\) \(qx^2-(p^2-2q)\,x+q=0\)
\(\Rightarrow\) \(qx^2+ (2q-p^2)\,x+q=0\)