# How do you solve 2( 9- 2y ) = 21?

Jan 3, 2018

$y = \frac{- 3}{4}$

#### Explanation:

$2 \left(9 - 2 y\right) = 21$

Let's start by using the distributive property

$\left(2\right) \left(9\right) + \left(2\right) \left(- 2 y\right) = 21$

$18 - 4 y = 21$

Then subtract $\textcolor{red}{18}$ from both sides

$\cancel{18} - 4 y - \cancel{\textcolor{red}{18}} = 21 - \textcolor{red}{18}$

$- 4 y = 3$

Then finally, divide both sides by $\textcolor{g r e e n}{- 4}$

$\frac{\cancel{- 4} y}{\cancel{\textcolor{g r e e n}{- 4}}} = \frac{3}{\textcolor{g r e e n}{- 4}}$

$y = \frac{- 3}{4}$

Jan 3, 2018

Graphical Interpritation...

#### Explanation:

Graphical Approach

Since $2 \left(9 - 2 y\right) = 21$

Both sides are equal to the same thing:

Let $x = 2 \left(9 - 2 y\right) \mathmr{and} x = 21$

Now sketching each of the functions...

Now the solution to the question is were the interesection is, hence lieing on both lines, and satifying each equation

So in this case, solving for $y$;

 color(blue)(y = -0.75 = -3/4