# Question to this algebra question?

## If f(x)=3x-1 and f(a)=5, what is the value of a

Jun 26, 2018

$a = 2$

#### Explanation:

If $f \left(x\right) = 3 x - 1$
then $f \left(a\right) = 3 a - 1$
and
since we are told $f \left(a\right) = 5$
we have $3 a - 1 = 5$

$\textcolor{w h i t e}{\text{xxxxx}} \Rightarrow 3 a = 6$

$\textcolor{w h i t e}{\text{xxxxx}} \Rightarrow a = 2$

Jun 26, 2018

$a = 2$

#### Explanation:

$f \left(a\right)$ means that there is some value $a$ that when I plug it into $f \left(x\right)$, it evaluates to $5$.

In other words, we are essentially being asked what is our input, when our output is $5$?

Let's set $f \left(x\right)$ equal to $5$:

$3 x - 1 = 5$

We can add $1$ to both sides and dividing the result by $2$ on both sides. We get

$x = 2$

Another way we can write this is

$f \left(2\right) = 5$

When we input $2$ into our function, we get $5$. Therefore,

$a = 2$

Hope this helps!