Question

Find the number to add to x^2-18x

Answer 1

Answer:

A. add 81; $(x-9)^2$

Step-by-step explanation:

The perfect square formula

$(a-b)^2=a^2-2ab+b^2$

Rewrite expression $x^2-18x$ as follows:

$x^2-2\cdot 9\cdot x$

So, to form a perfect square, $+9^2$ is missed.

When we add $9^2=81,$ we will get

$x^2-2\cdot 9\cdot x+9^2=(x-9)^2$