# Changing the subject involving division

• Sep 28th 2009, 01:16 AM
Meggomumsie
Changing the subject involving division
What is my first move please?

$\displaystyle y=\frac{5+x}{1-x}$
• Sep 28th 2009, 01:33 AM
Hello Meggomumsie
Quote:

Originally Posted by Meggomumsie
What is my first move please?

$\displaystyle y=\frac{5+x}{1-x}$

Get rid of fractions - always a good move in handling any equation. So, multiply both sides by $\displaystyle (1-x)$:

$\displaystyle y(1-x) = 5+x$

Then:

• Remove brackets on the LHS

• Collect terms in $\displaystyle x$ on one side only; everything else on the other side

• Take out a common factor of $\displaystyle x$ (by writing $\displaystyle x$ outside a bracket with the other bits inside)

Divide both sides by the resulting bracket to make $\displaystyle x$ the subject.

Can you complete it now?

• Sep 28th 2009, 05:21 AM
Meggomumsie
Thank you for your answer. I would still be pondering without your prompts as I have not been taught to factorise in the middle of changing the subject of a formula. So here is my attempt.

$\displaystyle y=\frac{5+x}{1-x}$

y(1 - x) = 5 + x

y - xy = 5 + x

y -5 = x + xy

y - 5 = x(1 + y)

$\displaystyle \frac{y-5}{y+1}=x$

It's great to be learning, thank you all ~ Marilyn
• Sep 28th 2009, 07:18 AM