# Math Help - changing the subject of a formula

1. ## changing the subject of a formula

P = ∏ (pie)r + 2r + 2a

2. Originally Posted by vtaylor
P = ∏ (pie)r + 2r + 2a
please say what you want to be the new subject, is it a or r?

3. ## sorry it is the r

oh im sorry it is the r

4. Originally Posted by vtaylor
P = ∏ (pie)r + 2r + 2a
changing the subject of the formula to r means we want to get r on one side of the equal sign by itself. a simple enough concept, in practice, it can be not so simple.

P = ∏r + 2r + 2a ..............first step, get rid of the 2a from the right
=> P - 2a
= ∏r + 2r ..........i subtracted 2a from both sides
=>
P - 2a = r(∏ + 2) ........i factored the r out
=> (P - 2a)/(
∏ + 2) = r ....i divided both sides by (∏ + 2)

so r =
(P - 2a)/(∏ + 2)