Is this the right answer?

rachael724

Junior Member
Joined
Sep 14, 2005
Messages
95
This is the problem:

If 1/R = 1/A + 1/B - 1/C , then R =

Is this the answer?

ABC/(BC - AC + AB)
 
Close, but you reversed a couple of signs. Check your work.

Eliz.
 
Then why all the question marks? That was my point. If you do all the steps clearly, there is no need for guessing or for question marks.

1/R = 1/A + 1/B - 1/C

LCD on the Right is ABC. Get all three fractions to that denominator.

1/R = BC/ABC + AC/ABC - AB/ABC = (BC + AC - AB)/ABC

Unless something is zero, then a/b = c/d implies b/a = d/c (If non-zero stuff is equal, so are the reciprocals)

R/1 = R = ABC/(BC + AC - AB)

Show EACH step, clearly, so that you will be able to read it tomorrow and tell what it was you did.
 
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