Question

Which number completes the square? x2 − 20x + _____?

Answer 1

Let's apply the following formula:

(x + a)^2 = x^2 + 2ax + a^2

We know that 2ax = -20x

Now, let's solve for a

First, let's divide both sides by 2.

ax = -10x

Now, let's divide both sides by x

a = -10

Now, let's square that value to find the number that completes the square.

a^2 = (-10)^2

a^2 = 100

The number that completes the square is 100.

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