# How do you multiply (x-9)^2?

Feb 13, 2016

Alternate method.
$= {x}^{2} - 18 x + 81$

#### Explanation:

We know that
${\left(a - b\right)}^{2} = {a}^{2} - 2 a b + {b}^{2}$
In the given question ${\left(x - 9\right)}^{2}$
$a = x \mathmr{and} b = 9$. Substituting the values we obtain
${\left(x - 9\right)}^{2} = {x}^{2} - 2 \cdot x \cdot 9 + {9}^{2}$

$\implies {x}^{2} - 18 x + 81$

Feb 13, 2016

${x}^{2} - 18 x + 81$

#### Explanation:

${\left(x - 9\right)}^{2}$

Remember the formula ${\left(a + b\right)}^{2} = {a}^{2} + 2 a b + {b}^{2}$

In this case $a = x , b = - 9$

And remember $- {9}^{2} = - 9 \cdot - 9 = 81$

Substitute the values:

We get:

$\Rightarrow {x}^{2} + 2 \left(x\right) \left(- 9\right) + 81$

$\Rightarrow = {x}^{2} - 18 x + 81$