Find two values for k so 4x^2 + kx + 81 = 0 has 2 solns

[Stine]

Find two values for k, for which the quadratic equation 4x^2 + kx + 81 = 0 has two equal real solutions

Oh I am lost!
:?

 

[Mrspi]

Re: Find two values for k

Find two values for k, for which the quadratic equation 4x^2+kx+81=0 has two equal real solutions

Oh I am lost!
:?

You haven't covered the discriminant in the quadratic formula yet? Most strange you'd be assigned this kind of problem........


The part of the quadratic formula which is under the radical sign, b<SUP>2</SUP> - 4ac, tells you what kind of roots a quadratic equation will have.

if
b<SUP>2</SUP> - 4ac = 0
the quadratic will have two equal real solutions.

In your equation, a = 4, b = k, and c = 81.

Substitute those values into
b<SUP>2</SUP> - 4ac = 0
and solve for k.