# Thread: maths in a program

1. ## maths in a program

Hi guys.
I know this isn't code but maths to go into a program, I need to know which is right.

I have a couple of formulae which need rearranging:

1) Make r the subject of.
a = 2pi(r + h)

first multiply out the bracket 2pir + 2pih = a

then subtract 2pih from both sides 2pir = a - 2pih

now divide both sides by 2pi r = a - 2pih / 2ip ( this is the answer that I have ).

2) make x the subject of.
5(x + 2) = y

first multiply out the bracket 5x + 10 = y

then subtract 10 from both sides 5x = y - 10

now divide both sides by 5 x = y - 10 / 5 ( stop here with this answer or do the maths on the right hand side giving x = y / 5 - 2 ) where do I stop with the answer.

in question 1 I stopped as soon as the required subject was on its own but in question 2 i got the required subject on its own and then proceeded to simplify the maths on the rhs (which way is correct)

THANKS for the help (learner wanting to be a master).

2. Firstly, you went the long way around to get 'r' and 'x' the subjects.

a= 2pi(r + h)
a/2pi = r+h
r = a/2pi -h

5(x + 2) = y
x + 2 = y/5
x = y/5 - 2

Simple. But if you understand the other way better stick to that. Second, if 'x' is the subject to be, go all the way, don't stop halfway through.

3. anthony,
kwigibo's answers are correct, whereas yours are missing parentheses. Your answers should be:
r = (a - 2pih) / 2pi
and
x = (y - 10) / 5,
which are equal to kwigibo's.

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