Question

What number must be added to the expression below to complete the square? x² - 18x

Answer 1

Answer:

$\boxed {\boxed {\sf 81}}$

Step-by-step explanation:

The standard form of a quadratic is:

$ax^2+bx+c$

To complete the square, the a (leading coefficient) must be 1 and there can only be terms with variables on one side.

The expression given:

$x^2-18x$

follows these rules. Next, we divide the b (linear coefficient) by 2, then square it. Basically:

$(\frac{b}{2})^2$

The b in the expression is -18.

$(\frac{-18}{2})^2$

$(-9)^2= -9*-9= 81$

This is the number that is added.