# Make x the subject

• Aug 7th 2010, 06:41 PM
DavidM
Make x the subject
Make x the subject:
$\displaystyle y = \frac{2x+7}{3x-1}$

I can't seem to make x the subject no matter how I re-arrange the equation.

• Aug 7th 2010, 06:51 PM
1005
Do you mean solve for x when you say "make x the subject"? I'd say the first step is definitely to multiply both sides by 3x - 1.
• Aug 7th 2010, 06:53 PM
undefined
Quote:

Originally Posted by DavidM
Make x the subject:
$\displaystyle y = \frac{2x+7}{3x-1}$

I can't seem to make x the subject no matter how I re-arrange the equation.

Multiply both sides by (3x-1), then expand all terms (you will get 3xy-y on the LHS), gather all terms with x in them on one side (move other terms to the other side), factor out the x, divide both sides by the quantity that x is multplying.
• Aug 7th 2010, 06:53 PM
DavidM
I mean make x the subject as in:

$\displaystyle x = ?$

Re-arrange the formula to get x on its own.
• Aug 7th 2010, 06:57 PM
DavidM
Got it, thanks undefined.

$\displaystyle x = \frac {y+7}{3y-2}$
• Aug 8th 2010, 07:04 AM
1005
Quote:

Originally Posted by DavidM
Got it, thanks undefined.

$\displaystyle x = \frac {y+7}{3y-2}$

you asked for a hint and then thank the guy who gave you the answer instead of a nudge in the right direction.
• Aug 8th 2010, 07:54 AM
undefined
Quote:

Originally Posted by 1005
you asked for a hint and then thank the guy who gave you the answer instead of a nudge in the right direction.

There are many cases of unbalanced thanks here on the forum, sometimes I'm unduly appreciated, sometimes underappreciated, it is what it is.

I agree that your reply does more of what the OP asked than mine and that you deserve credit.

If anyone wants a (somewhat lengthy) explanation of my action, it is: I just made a judgment call that the question was of the "you either see it or you don't" type or "there's a trick to it" type, and that the response "here's the trick; observe" could be useful to the OP; also, I made a response that I thought would be helpful to me if I were in the OP's position; and I have no opinion on whether giving a "very large hint" like mine or a small hint like 1005's is better or worse, or right or wrong, to me they're just different approaches of people who want to help out.