Home
Class 12
MATHS
If the roots of equation x^(3) + ax^(2) ...

If the roots of equation `x^(3) + ax^(2) + b = 0 are alpha _(1), alpha_(2), and `
` alpha_(3) (a , b ne 0)`. Then find the equation whose roots are
`(alpha_(1)alpha_(2)+alpha_(2)alpha_(3))/(alpha_(1)alpha_(2)alpha_(3)), (alpha_(2)alpha_(3)+alpha_(3)alpha_(1))/(alpha_(1)alpha_(2)alpha_(3)), (alpha_(1)alpha_(3)+alpha_(1)alpha_(2))/(alpha_(1)alpha_(2)alpha_(3)) `.

Text Solution

AI Generated Solution

The correct Answer is:
To solve the given problem, we need to find the equation whose roots are given in terms of the roots of the original cubic equation. Let's denote the roots of the original equation \( x^3 + ax^2 + b = 0 \) as \( \alpha_1, \alpha_2, \alpha_3 \). ### Step 1: Identify the roots of the new equation The roots of the new equation are given as: 1. \( \frac{\alpha_1 \alpha_2 + \alpha_2 \alpha_3}{\alpha_1 \alpha_2 \alpha_3} \) 2. \( \frac{\alpha_2 \alpha_3 + \alpha_3 \alpha_1}{\alpha_1 \alpha_2 \alpha_3} \) 3. \( \frac{\alpha_1 \alpha_3 + \alpha_1 \alpha_2}{\alpha_1 \alpha_2 \alpha_3} \) Let \( p = \alpha_1 \alpha_2 \alpha_3 \) (the product of the roots), \( q = \alpha_1 \alpha_2 + \alpha_2 \alpha_3 + \alpha_3 \alpha_1 \) (the sum of the products of the roots taken two at a time), and \( r = \alpha_1 + \alpha_2 + \alpha_3 \) (the sum of the roots). ### Step 2: Express the new roots in terms of \( p, q, r \) The new roots can be rewritten as: 1. \( \frac{q - \alpha_3^2}{p} \) 2. \( \frac{q - \alpha_1^2}{p} \) 3. \( \frac{q - \alpha_2^2}{p} \) ### Step 3: Find the sum of the new roots The sum of the new roots can be calculated as follows: \[ \text{Sum} = \frac{(q - \alpha_3^2) + (q - \alpha_1^2) + (q - \alpha_2^2)}{p} = \frac{3q - (\alpha_1^2 + \alpha_2^2 + \alpha_3^2)}{p} \] Using the identity \( \alpha_1^2 + \alpha_2^2 + \alpha_3^2 = r^2 - 2q \), we can substitute: \[ \text{Sum} = \frac{3q - (r^2 - 2q)}{p} = \frac{5q - r^2}{p} \] ### Step 4: Find the sum of the products of the new roots taken two at a time The sum of the products of the new roots taken two at a time is given by: \[ \text{Product Sum} = \frac{(\frac{q - \alpha_3^2}{p})(\frac{q - \alpha_1^2}{p}) + (\frac{q - \alpha_2^2}{p})(\frac{q - \alpha_3^2}{p}) + (\frac{q - \alpha_1^2}{p})(\frac{q - \alpha_2^2}{p})}{p^2} \] This simplifies to: \[ \text{Product Sum} = \frac{(q^2 - q(\alpha_1^2 + \alpha_2^2 + \alpha_3^2) + \alpha_1^2 \alpha_2^2 + \alpha_2^2 \alpha_3^2 + \alpha_3^2 \alpha_1^2)}{p^2} \] Using \( \alpha_1^2 + \alpha_2^2 + \alpha_3^2 = r^2 - 2q \) again, we can substitute: \[ \text{Product Sum} = \frac{(q^2 - q(r^2 - 2q) + \text{(sum of squares of products)})}{p^2} \] ### Step 5: Find the product of the new roots The product of the new roots is: \[ \text{Product} = \frac{(q - \alpha_1^2)(q - \alpha_2^2)(q - \alpha_3^2)}{p^3} \] ### Step 6: Form the new polynomial Using Vieta's formulas, we can form the new polynomial with roots as calculated above: \[ x^3 - \left(\frac{5q - r^2}{p}\right)x^2 + \left(\text{Product Sum}\right)x - \left(\text{Product}\right) = 0 \] ### Final Equation Thus, the final equation whose roots are the specified transformations of the original roots is: \[ x^3 - \frac{5q - r^2}{p}x^2 + \left(\text{Product Sum}\right)x - \left(\text{Product}\right) = 0 \]

To solve the given problem, we need to find the equation whose roots are given in terms of the roots of the original cubic equation. Let's denote the roots of the original equation \( x^3 + ax^2 + b = 0 \) as \( \alpha_1, \alpha_2, \alpha_3 \). ### Step 1: Identify the roots of the new equation The roots of the new equation are given as: 1. \( \frac{\alpha_1 \alpha_2 + \alpha_2 \alpha_3}{\alpha_1 \alpha_2 \alpha_3} \) 2. \( \frac{\alpha_2 \alpha_3 + \alpha_3 \alpha_1}{\alpha_1 \alpha_2 \alpha_3} \) 3. \( \frac{\alpha_1 \alpha_3 + \alpha_1 \alpha_2}{\alpha_1 \alpha_2 \alpha_3} \) ...
Promotional Banner

Topper's Solved these Questions

  • THEORY OF EQUATIONS

    CENGAGE|Exercise Exercise 2.12|11 Videos
  • THEORY OF EQUATIONS

    CENGAGE|Exercise Exercise 2.13|9 Videos
  • THEORY OF EQUATIONS

    CENGAGE|Exercise Exercise 2.10|5 Videos
  • STRAIGHT LINES

    CENGAGE|Exercise JEE Advanced Previous Year|4 Videos
  • THREE DIMENSIONAL GEOMETRY

    CENGAGE|Exercise Question Bank|20 Videos

Similar Questions

Explore conceptually related problems

If the roots of equation x^3+a x^2+b=0a r ealpha_1,alpha_2 and alpha_3(a ,b!=0) , then find the equation whose roots are (alpha_1alpha_2+alpha_2alpha_3)/(alpha_1alpha_2alpha_3),(alpha_2alpha_3+alpha_3alpha_1)/(alpha_1alpha_2alpha_3),(alpha_1alpha_3+alpha_1alpha_2)/(alpha_1alpha_2alpha_3)

If alpha_(2)

if sqrt(alpha_(1)-1)+2sqrt(alpha_(2)-4)+3sqrt(alpha_(3)-9)+4sqrt(alpha_(4)-16)=(alpha_(1)+alpha_(2)+alpha_(3)+alpha_(4))/(2) where alpha_(1),alpha_(2),alpha_(3),alpha_(4) are all real. Then

If alpha_(1),,alpha_(2),...,alpha_(n) are the roots of equation x^(n)+nax-b=0, show that (alpha_(1)-alpha_(2))(alpha_(1)-alpha_(2))...(alpha_(1)-alpha_(n))=n(alpha_(1)^(n-1)+a)

If alpha is an imaginary roots of x^(5)-1=0, then the equation whose roots are alpha+alpha^(4) and alpha^(2)+alpha^(3) is

If alpha!=beta but alpha^(2)=5 alpha-3,beta^(2)=5 beta-3, then find the equation whose roots are (alpha)/(beta) and (beta)/(alpha)

Find the coefficient of alpha^(6) in the product (1+alpha+alpha^(2))(1+alpha+alpha^(2))(1+alpha+alpha^(2)+alpha^(3)) (1+alpha)(1+alpha)(1+alpha) .

If alpha!=beta and alpha^(2)=5 alpha-3 and beta^(2)=5 beta-3. find the equation whose roots are alpha/ beta and beta/ alpha .

If alpha_(1),alpha_(2),alpha_(3)......alpha_(n) are roots of the equation f(x)=0 then (-alpha_(1),-alpha_(2),-alpha_(3),......alpha_(n)) are the roots of