Step-by-step explanation:
Since x² + kx + (k + 3) is tangent to the x-axis, the quadratic function has a repeated root.
The discriminant is zero, so b² - 4ac = 0.
=> k² - 4(1)(k + 3) = 0
=> k² - 4k - 12 = 0
=> (k - 6)(k + 2) = 0
Hence k = 6 or k = -2.
