Question
A polynomial ψ(s) = ansn + an-1sn-1 + ......+ a1s + a0 of degree n > 3 with constant real coefficients an, an-1, ... a0 has triple roots at s = -σ. Which one of the following conditions must be satisfied?
Options :
ψ(s) = 0 at all the three values of s satisfying s3 + σ3 = 0
ψ(s) = 0, and at s = -σ
ψ(s) = 0, and at s = -σ
ψ(s) = 0, at s = -σ
Answer :
ψ(s) = 0, and at s = -σ
Solution :
Polynomial, ψ(s) = ansn + an-1sn-1 + ......+ a1s + a0 of degree n > 3
It has triple root at s = -σ
so, at s = -σ
ψ(s) will be equal to zero, because it is a root of the polynomial
ψ(s) = ψ(-σ) = 0
Since polynomial ψ(s) has triple root at s = -σ
So, (s + σ)3 is one factor of polynomial
Since the factor has a cube, it will have an inflexion point in the curve as the x3 has.
Hence first and second-order derivatives will be zero at the point of inflexion.
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