When using the Quadratic Formula, how can you tell when a quadratic equation has only one solution/one x-intercept? When the discriminant (b2 - 4ac) is negative

When b in the quadratic formula is greater than the discriminant (b2 - 4ac).

When the discriminant (b2 - 4ac) equals zero

When the discriminant (b2 - 4ac) is not a perfect square