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

2 Answers

Jun 26, 2018

$a = 2$ $a=2$

Explanation:

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

$xxxxx \Rightarrow 3 a = 6$ $color(white)("xxxxx")rArr 3a=6$

$xxxxx \Rightarrow a = 2$ $color(white)("xxxxx")rArr a=2$

Jun 26, 2018

$a = 2$ $a=2$

Explanation:

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

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

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

$3 x - 1 = 5$ $3x-1=5$

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

$x = 2$ $x=2$

Another way we can write this is

$f (2) = 5$ $f(2)=5$

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

$a = 2$ $a=2$

Hope this helps!

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