Question Details

The roots of the equation  a x 3 - 24 x 2 + 188 x - 480 = 0  are three consecutive even natural numbers. The value of  a  is __________.

Options

A

2

B

1

C

3

D

4

Show Answer

Correct Answer :

Option B

1

Solution :

The correct option is 1.

We are given a cubic equation:
a x 3 - 24 x 2 + 188 x - 480 = 0

Let the roots of this cubic equation be three consecutive even natural numbers. We can denote these roots as:
α = 2 k - 2 , β = 2 k , γ = 2 k + 2 where k is an integer such that k2 (so that the roots are positive even integers, i.e., natural numbers).

For a standard cubic equation of the form ax3+bx2+cx+d=0 with roots α, β, and γ, the relations between the coefficients and the roots are given by Vieta's formulas:
1. Sum of the roots:
α + β + γ = - b a = 24 a 2. Sum of the product of roots taken two at a time:
α β + β γ + γ α = c a = 188 a 3. Product of the roots:
α β γ = - d a = 480 a

Substituting the expressions for the roots in terms of k into the first relation:
( 2 k - 2 ) + 2 k + ( 2 k + 2 ) = 24 a Simplifying the left-hand side:
6 k = 24 a a = 4 k

Now, substitute this relation a=4k into the third relation (product of the roots):
( 2 k - 2 ) ( 2 k ) ( 2 k + 2 ) = 480 a Using the identity (2k-2)(2k+2)=4k2-4, we have:
2 k ( 4 k 2 - 4 ) = 480 ( 4 / k ) 8 k ( k 2 - 1 ) = 120 k

Since the roots are consecutive natural numbers, we know that k>0. We can safely divide both sides by 8k:
k 2 - 1 = 15 k 2 = 16 Since k must be a positive integer for the roots to be positive natural numbers, we take:
k = 4

Substituting k=4 back into our equation for a:
a = 4 k = 4 4 = 1

Thus, the value of a is 1.

Unlock Our Free Library

Access expert-curated educational resources and study materials—completely free.

Discover more resources

You may also like

Mock Tests

View All
  • CTET
  • intermediate
  • No time limit
  • child development and pedagogy, mathematics, social science

  • SSC
  • intermediate
  • 2 hours and 30 mins
  • child development and pedagogy, mathematics, social science

Ask AI Tutor
5 left
Q1 View Question & Options
AI Tutor is solving this question...
Reading question context & options...