help maths problem

mary21 · 19-09-2011 06:27PM #1

i just cant figure how to do this it is doing my head in!! please help

formulae- simulaneous equations

x= a+b
----
.......... a-b

make a subject to the formula

I know the answer is a=b(x+1)

x-1

MathsManiac · 23-09-2011 08:54PM

Multiply both sides by (a-b) to give:
x(a-b) = (a+b)

Expand the left-hand side to get:

xa - xb = a + b

Next, you need to get all terms that have an "a" in them to the left-hand side, and all other terms to the right-hand side. So, add xb to both sides:

xa = a + b + xb

...and subtract a from both sides:

xa - a = b + xb.

Factorsie the left-hand side, so that a will appear only once:

a(x - 1) = b + xb.

(We could have factorised the right-hand side too, but it's not necessary.)
Now divide across by (x - 1) to get:

a = (b + xb) / (x-1)

If we had factorised the top line too, this would be a = b(x+1)/(x-1).

mary21 · 23-09-2011 09:45PM

thank you so much:)

Syllabus · 23-09-2011 09:49PM

MathsManiac wrote: »

Multiply both sides by (a-b) to give:
x(a-b) = (a+b)

Expand the left-hand side to get:

xa - xb = a + b

Next, you need to get all terms that have an "a" in them to the left-hand side, and all other terms to the right-hand side. So, add xb to both sides:

xa = a + b + xb

...and subtract a from both sides:

xa - a = b + xb.

Factorsie the left-hand side, so that a will appear only once:

a(x - 1) = b + xb.

(We could have factorised the right-hand side too, but it's not necessary.)
Now divide across by (x - 1) to get:

a = (b + xb) / (x-1)

If we had factorised the top line too, this would be a = b(x+1)/(x-1).

my head hurts:eek:

matthew8 · 24-09-2011 02:01PM

Wait, from reading the op I have no idea of what the actual equation is.

spurious · 24-09-2011 02:06PM

Asked and answered.
Closed.

help maths problem

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