If λ ∈ R is such that the sum of the cubes of the roots of the equation, x^2+(2-λ) x+(10-λ)=0 is minimum, then the magnitude of the difference of the…
JEE Main 2018 — Mathematics Algebra
2018mcqeasy
If λ∈R is such that the sum of the cubes of the roots of the equation, x2+(2−λ)x+(10−λ)=0 is minimum, then the magnitude of the difference of the roots of this equation is
Official previous-year question
Held on 15 Apr 2018 · Verified 6 Jul 2026.
Options
A
20
B
25
C
27
D
42
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Solution
Let, the roots of the equation, x2+(2−λ)x+(10−λ)=0 are α and β. Also roots of the given equation are 2λ−2±4−4λ+λ2−40+4λ=2λ−2±λ2−36 The magnitude of the difference of the roots is λ2−36 So, α3+β3=4(λ−2)3+43(λ−2)(λ2−36)=4(λ−2)(4λ2−4λ−104)=(λ−2)(λ2−λ−26)=f(λ) As f(λ) attains its minimum value at λ=4. Therefore, the magintude of the difference of the
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