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

In summary, there are an infinite number of integral values of 'k' for which the quadratic equation 2x^2 + kx - 4=0 will have two rational solutions. This is because the discriminant, k^2+32, can be written as n^2-k^2, and there are an infinite number of ways to factor 32 into two numbers with a difference of 2k+1. Therefore, there is no specific value of 'k' for which the equation will have two rational solutions.
  • #1
ritwik06
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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?
 
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  • #2
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?
 
  • #3
n is at least k+1, so n^2-k^2 >= (k+1)^2 - k^2 = 2k + 1
 

1. What is a quadratic equation?

A quadratic equation is a mathematical expression in the form of ax² + bx + c = 0, where a, b, and c are constants and x is the variable. It is a polynomial equation of degree 2, and its graph forms a parabola.

2. How do you find the integral values of 'k' for 2 rational solutions?

To find the integral values of 'k' for 2 rational solutions, we first need to set the quadratic equation equal to 0. Then, we can use the quadratic formula: x = (-b ± √(b²-4ac)) / 2a. The value of 'k' will be the constant 'a' in this formula. We can then solve for 'k' by plugging in the known values for 'a', 'b', and 'c'.

3. What is the significance of having 2 rational solutions in a quadratic equation?

Having 2 rational solutions in a quadratic equation means that the graph of the equation will intersect the x-axis at 2 distinct points. This also means that the equation can be factored into 2 linear expressions, making it easier to solve.

4. Can a quadratic equation have more than 2 rational solutions?

No, a quadratic equation can have at most 2 rational solutions. This is because a quadratic equation is a polynomial equation of degree 2, and according to the Fundamental Theorem of Algebra, a polynomial of degree n can have at most n complex solutions. Since rational numbers are a subset of complex numbers, this means that a quadratic equation can have at most 2 rational solutions.

5. What does it mean if the quadratic equation has no rational solutions?

If a quadratic equation has no rational solutions, it means that the graph of the equation does not intersect the x-axis, or in other words, it has no real roots. This can happen if the discriminant (b²-4ac) is negative, or if the equation cannot be factored into 2 linear expressions with rational coefficients.

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