Question

For which positive integer values of $k$ does $kx^2+20x+k=0$ have rational solutions? Express your answers separated by commas and in increasing order.

Answer 1

Answer:

-10,10

Step-by-step explanation:

The given quadratic equation is

$k {x}^{2} + 20x + k = 0$

The discriminant of this equation is given by;

$D = {b}^{2} - 4ac$

where a=k, b=20, c=k

For rational solutions, the discriminant must be zero.

${20}^{2} - 4 \times k \times k = 0$

Simplify to get:

$400 - 4 {k}^{2} = 0$

This implies that:

$400 = 4 {k}^{2}$

$100 = {k}^{2}$

Take square root to get:

$k = \pm\sqrt{100}$

$k = \pm10$

$k = - 10 \: or \: k = 10$