Answer:
[tex]\boxed {\boxed {\sf 81}}[/tex]
Step-by-step explanation:
The standard form of a quadratic is:
[tex]ax^2+bx+c[/tex]
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:
[tex]x^2-18x[/tex]
follows these rules. Next, we divide the b (linear coefficient) by 2, then square it. Basically:
[tex](\frac{b}{2})^2[/tex]
The b in the expression is -18.
[tex](\frac{-18}{2})^2[/tex]
[tex](-9)^2= -9*-9= 81[/tex]
This is the number that is added.
