SOLUTION: solve for r S = a / (a - r) I know the answer but don't know how to get it

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Question 227346: solve for r S = a / (a - r) I know the answer but don't know how to get it
Answer by rapaljer(4671) About Me  (Show Source):
You can put this solution on YOUR website!
S=a%2F%28a-r%29+ Solve for r.

Multiply both sides of the equation by the denominator (a-r).

S%28a-r%29=+%28a-r%29%2A%28a%2F%28a-r%29%29+
Sa-Sr=+a

Get the r term alone on the left side by subtracting Sa from each side:
Sa-Sa-Sr=a-Sa

-Sr=a-Sa

Divide both sides by -S:
%28-Sr%29%2F%28-S%29+=+%28a-Sa%29%2F%28-S%29+

Multiply numerator and denominator by -1:
r=+%28-a%2BSa%29%2FS or r=%28Sa-a%29%2FS or r=%28a%28S-1%29%29%2FS

You may want to take a look at my own website for my non-traditional explanation of the topic that I call "Literal Equations". Do a "Bing" or "Google" search for my last name "Rapalje". Look for "Rapalje Homepage" near the top of these searches. Then near the top of my Homepage, look for "Basic, Intermediate and College Algebra". Choose either Basic Algebra" Chapter 3", "Section 3.07". For a slightly more advanced explanation, see "Intermediate Algebra", "Chapter 2", "Section 2.07".

As to your specific problem that you posted, I don't think you gave enough information to solve it.

R^2

Dr. Robert J. Rapalje, Retired
Seminole State College of Florida
Altamonte Springs Campus