Simplifying Equations

[oudielokda5640]

In Chapter 3 page 7 there is an example for getting rid of variables in denominators.

It says ' When there are different denominators containing variables cross multiply the denominator to cancel out'

I am confused about this, which denominator am I supposed to cross multiply and what am I supposed to cross mulitply it with?

The example goes on to multiply 3x first to the whole equation then multiplies (x + 3) to the new equation.

Can you please explain, am I essentially supposed to multiply each denominator seperatly to the whole equation, i.e multiply 3x first to the whole equation then multiply (x + 3) to the whole equation or is there something else I need to do?

Also is this a general rule that i should apply i.e multiply each denominator seperately to the whole equation untl all denominators are multipled to the equation?

Please let me know.

Thanks,
Mohamed

[goldstanda3269]

"Can you please explain, am I essentially supposed to multiply each denominator seperatly to the whole equation, i.e multiply 3x first to the whole equation then multiply (x + 3) to the whole equation or is there something else I need to do?"

You are exactly correct.


"Also is this a general rule that i should apply i.e multiply each denominator seperately to the whole equation untl all denominators are multipled to the equation?"

Actually, just before that problem, the general rule is given (Maths 3.2.2; page GM-79, or as you say, page 7): "When there are different denominators containing variables".

The reason that rule is stated is because, sometimes, if there are only numbers in the denominator, it might not be necessary to remove the denominator. For example, if the fraction is 3/2, you might decide to rewrite 3/2 as 1.5 instead of multiplying both sides by 2. However, if it is 3/(2x) then you need to get rid of the variable x in the denominator so multiply both sides by 2x.