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If α and β are roots of x\(^2\) + mx - n = 0, where...

Further Mathematics
WAEC 2022

If α and β are roots of x\(^2\) + mx - n = 0, where m and n are constants, form the

equation whose roots are 1
α
and 1
β
.
  • A. mnx\(^2\)  - n\(^2\) x - m = 0
  • B. mx\(^2\)  - nx + 1 = 0
  • C. nx\(^2\)  - mx + 1 = 0
  • D. nx\(^2\)  - mx - 1 = 0
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Correct Answer: Option D
Explanation

x\(^2\) + mx - n = 0

a = 1, b = m, c = -n

α + β = \(\frac{-b}{a}\) = \(\frac{-m}{1}\) = -m

αβ = \(\frac{c}{a}\) = \(\frac{-n}{1}\) = -n

the roots are = \(\frac{1}{α}\) and \(\frac{1}{β}\)

sum of the roots = \(\frac{1}{α}\) + \(\frac{1}{β}\)

\(\frac{1}{α}\) + \(\frac{1}{β}\) = \(\frac{α+β}{αβ}\)

α + β = -m
αβ = -n

\(\frac{α+β}{αβ}\) = \(\frac{-m}{-n}\) → \(\frac{m}{n}\)

product of the roots = \(\frac{1}{α}\) * \(\frac{1}{β}\)

\(\frac{1}{α}\) + \(\frac{1}{β}\) = \(\frac{1}{αβ}\) → \(\frac{1}{-n}\)

x\(^2\) - (sum of roots)x + (product of roots)
x\(^2\) - ( m/n )x + ( 1/-n ) = 0
multiply through by n
nx\(^2\) - mx - 1 = 0

 


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