# Thread: find the set of values...?

1. ## find the set of values...?

Find the set of values of k for which the equation 2x(sqrd) + kx + 2 = 0 has no real roots.

i have no idea how to solve this... can somone please explain?

thanks

2. Originally Posted by RubbishAtMaths
Find the set of values of k for which the equation 2x(sqrd) + kx + 2 = 0 has no real roots.

i have no idea how to solve this... can somone please explain?

thanks
A quadratic equation of the form $\displaystyle ax^2+bc+c = 0$ has no real roots when its discriminant ($\displaystyle b^2-4ac$) is less than 0.

In other word, you have to find values of k for which:

$\displaystyle k^2-4(2)(2) < 0$

3. Originally Posted by Mush
A quadratic equation of the form $\displaystyle ax^2+bc+c = 0$ has no real roots when its discriminant ($\displaystyle b^2-4ac$) is less than 0.

In other word, you have to find values of k for which:

$\displaystyle k^2-4(2)(2) < 0$
$\displaystyle k^2 < 16$ so is the answer $\displaystyle -4 < k < 4$?

4. Originally Posted by RubbishAtMaths
$\displaystyle k^2 < 16$ so is the answer $\displaystyle -4 < k < 4$?
Yep!