The quadratic equation $2x^2 + bx + 18 = 0$ has a double root. Find all possible values of $b.$
Complete the square, to get 2(x + 3)^2 = 2x^2 + 6x + 18 ==> b = 6.
If we have a double root.....the discriminant = 0
So
b^2 - 4 *2 * 18 = 0
b^2 -144 = 0
b^2 = 144
b = 12 or b = -12
