Question

If using the method of completing the square to solve the quadratic equation

x? + 15x + 25 = 0, which number would have to be added to "complete the
square"?

Answer 1

31.25

Explanation:

The general form of a complete square would be (x + a)^2 + b

Given an equation of X^2 + 15X + 25 = 0,

the idea is to reduce it into the form if (X + C)^2

which can be expanded into X^2 + 2XC + C^2

In this case 15 will be our 2C So our c will be 7.5.

Substituting in these numbers,

We have X^2 + 15X + (7.5)^2 = 0

However our original equation has 25 for its C^2, thus

we need to add 31.25 in order to get (7.5)^2

FYI

The final completed form will be (X + 7.5)^2 - 31.25