Mark the correct alternative in the following:
If the polynomial equation a0xn + an–1xn–1 + an–2xn–2 + …. a2x2 + a1x + a0 = 0
n being a positive integer, has two different real roots α and β, then between α and β, the equation n anxn–1 + (n–1) an–1xn–2 + … + a1 = 0 has
As the polynomial, nanxn–1 + (n–1) an–1xn–2 + … + a1 = 0 is a derivative of the polynomial a0xn + an – 1xn – 1 + an – 2xn – 2 +..............a2x2 + a1x + a0 = 0 --------- (i)
Putting x = 0 in equation (i),
f(0) = a0 < 0, {Y – Intercept of the graph is negative}
On the other hand, an > 0 and ‘n’ is even, the leading term on xn, is positive for only x.
For |x| to be large, the term anxn will dominate, so
lim x→-∞ f (x) = +∞
lim x→+∞ f (x) = +∞
If lim x→+∞ f (x) = +∞, there must exist
Same number α < 0, where f(α > 0)
f(0) = a0 < 0,
α < β < 0, such that f(β) = 0
Also, there is some value 0 < α,
Where f(a) & so there exists,
0 < b < a with f(b) = 0
Additionally, the polynomial function (equation (i)) is continuous everywhere in R and consequently derivative in R.
a0xn + an – 1xn – 1 + an – 2xn – 2 +..............a2x2 + a1x + a0 = 0 is continuous on α,β and derivative on α,β.
Thus, it satisfies both the conditions of Rolle' s Theorem.
As per the Rolle’s Theorem, between any two roots of a function f(x), there exists at least one root of its derivative.
Thus, the equation nanxn–1 + (n–1) an–1xn–2 + … + a1 = 0 will have at least one root between α & β.
Hence, Option (C) is the answer.