Quadratic Equations: Find Integral Values of 'k' for 2 Rational Solutions

Click For Summary
SUMMARY

The discussion focuses on determining the integral values of 'k' for the quadratic equation 2x² + kx - 4 = 0 to yield two rational solutions. The key condition for rational solutions is that the discriminant, calculated as d = k² + 32, must be a perfect square. The equation n² - k² = 32 is derived, leading to the factorization (n - k)(n + k) = 32. The analysis reveals that n must be greater than k, establishing a relationship that constrains the values of 'k' to be evaluated.

PREREQUISITES
  • Understanding of quadratic equations and their properties
  • Familiarity with the discriminant and its role in determining the nature of roots
  • Basic algebraic manipulation and factorization techniques
  • Knowledge of perfect squares and integer solutions
NEXT STEPS
  • Explore the properties of quadratic equations and their discriminants
  • Study the concept of perfect squares and integer factorization
  • Investigate methods for solving Diophantine equations
  • Learn about the implications of rational roots in polynomial equations
USEFUL FOR

Students studying algebra, particularly those tackling quadratic equations, educators teaching mathematical concepts, and anyone interested in the properties of rational solutions in polynomial equations.

ritwik06
Messages
577
Reaction score
0

Homework Statement


Find the number of integral values of 'k' for which the quadratic equation 2x^2 +kx - 4=0 will have two rational solutions.


Homework Equations



d=(b^2- 4ac)^(1/2)

The Attempt at a Solution



If discriminant is a perfect square, then the roots will be rational and unequal. but for how many values of 'k' starting from 2 itself will I check th discriminant to be a perfect square?
 
Physics news on Phys.org
The discriminant is k^2+32. So k^2+32=n^2 where n is an integer. n^2-k^2=32. But n^2-k^2=(n-k)*(n+k). How high do you need to check?
 
n is at least k+1, so n^2-k^2 >= (k+1)^2 - k^2 = 2k + 1
 

Similar threads

  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 22 ·
Replies
22
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
7
Views
2K
  • · Replies 20 ·
Replies
20
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K