Math Problem Statement

If one root of the equation x^2 + kx - 8 = 0 is the square of the other, what is the value of k?

Solution

The question shown is in Hindi and translates to:

"If one root of the equation x2+kx8=0x^2 + kx - 8 = 0 is the square of the other root, what is the value of kk?"

Let's solve this step by step.

Given equation:

x2+kx8=0x^2 + kx - 8 = 0

Let the roots of this quadratic equation be α\alpha and β\beta. We are told that one root is the square of the other, i.e., α=β2\alpha = \beta^2 or β=α2\beta = \alpha^2.

From Vieta’s formulas for a quadratic equation ax2+bx+c=0ax^2 + bx + c = 0, the relationships between the coefficients and the roots are:

  • Sum of roots: α+β=k1=k\alpha + \beta = -\frac{k}{1} = -k
  • Product of roots: αβ=81=8\alpha \cdot \beta = -\frac{-8}{1} = 8

Now, using the condition that one root is the square of the other, say α=β2\alpha = \beta^2.

Thus, substituting α=β2\alpha = \beta^2 into the sum and product formulas:

  1. α+β=β2+β=k\alpha + \beta = \beta^2 + \beta = -k
  2. αβ=β2β=β3=8\alpha \cdot \beta = \beta^2 \cdot \beta = \beta^3 = 8

From the second equation, we get: β3=8    β=2\beta^3 = 8 \implies \beta = 2

Now substitute β=2\beta = 2 into the sum equation: β2+β=k    22+2=k    4+2=k    k=6\beta^2 + \beta = -k \implies 2^2 + 2 = -k \implies 4 + 2 = -k \implies k = -6

Therefore, the value of kk is -6.

However, looking at the provided options, none of them include 6-6. Let me re-check the method or see if the phrasing might involve a simplification step. Would you like to go deeper into the review or explore why the answer isn't listed?

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Quadratic Equations
Algebra

Formulas

Vieta's relations: Sum of roots = -b/a, Product of roots = c/a
Quadratic equation formula: ax^2 + bx + c = 0

Theorems

Vieta's Formulas
Quadratic Equations

Suitable Grade Level

Grades 9-10