# find the set of values...?

• Jan 7th 2009, 11:52 AM
RubbishAtMaths
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
• Jan 7th 2009, 11:58 AM
Mush
Quote:

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 $ax^2+bc+c = 0$ has no real roots when its discriminant ( $b^2-4ac$) is less than 0.

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

$k^2-4(2)(2) < 0$
• Jan 7th 2009, 12:10 PM
RubbishAtMaths
Quote:

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

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

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

$k^2 < 16$ so is the answer $-4 < k < 4$?
• Jan 7th 2009, 12:15 PM
Mush
Quote:

Originally Posted by RubbishAtMaths
$k^2 < 16$ so is the answer $-4 < k < 4$?

Yep!