# Thread: Changing the subject question help!

1. ## Changing the subject question help!

I need to make a the subject, but i keep ending up with 0 a's. Can someone please give a step by step to how they did it if they know the answer.

And thankyou to anyone in advanced.

b = (a + x) / (a + c)

edit: the right side is meant to be a fraction, but the best way i can think of writing is is with a '/'.

2. Originally Posted by nugiboy
I need to make a the subject, but i keep ending up with 0 a's. Can someone please give a step by step to how they did it if they know the answer.

And thankyou to anyone in advanced.

b = (a + x) / (a + c)

edit: the right side is meant to be a fraction, but the best way i can think of writing is is with a '/'.
$\displaystyle b = \frac{a + x}{a + c}$

$\displaystyle b(a + c) = a + x$

$\displaystyle ab + bc = a + x$

$\displaystyle ab - a = x - bc$

$\displaystyle a(b - 1) = x - bc$

$\displaystyle a = \frac{x - bc}{b - 1}$

Of course, we need to recall that $\displaystyle a \neq -c$ else the original expression can't exist.

-Dan

3. Originally Posted by nugiboy
I need to make a the subject, but i keep ending up with 0 a's. Can someone please give a step by step to how they did it if they know the answer.

And thankyou to anyone in advanced.

b = (a + x) / (a + c)

edit: the right side is meant to be a fraction, but the best way i can think of writing is is with a '/'.
$\displaystyle b=\frac{a+x}{a+c}$

So:

$\displaystyle (a+c)b=a+x$

or:

$\displaystyle (b-1)a=x-cb$

so:

$\displaystyle a=\frac{x-cb}{b-1}$

RonL