What is the value of b if the following quadratic equation has equal roots: 4x^2 + bx + 18 =0

Given that 4x^2+bx+18 = 0 is a quadratic equation whose
roots are equal. To find the value of b.

If Ax^2+Bx+C = 0
has equal roots, then the discriminant D  B^2-4AC = 0.

In
this case A = 4, B = b and C = 18.

Therefore B^2-4AC = 0
implies b^2-4*4*18 = 0.

b^2 =
4^2*18

Therefore b = +sqrt (4^2*18) , b= - sqrt
(4^2*18)

So  b = 4*3sqrt2 , b =
-4*3*sqrt2.

Therefore b = 12sqrt2, or b=
-12sqrt2.