Which number completes the square for the expression x squared plus 14x?

1. Completing the square adds the square of half the coefficient of x. 2. The coefficient of x here is 14, and half of 14 is 7. 3. Squaring 7 gives 49, so 49 is the number to add. 4. Adding 28 doubles instead of squaring, and the result would not factor as a perfect square. _Source: OpenStax Intermediate Algebra (CC BY 4.0), section 9.2 Solve Quadratic Equations by Completing the Square_