TuanNguyen87 wrote:In an electric circuit, two resistors with resistances x and y are connected in parallel. In this case, if r is the combined resistance of these two resistors, then the reciprocal of r is equal to the sum of the reciprocals of x and y. What is r in terms of x and y?
A. xy
B. x + y
C. 1/(x+y)
D. xy/(x+y)
E. (x+y)/xy
Answer: D
Thanks a lot in advance!!!
We can plug in values for x and y.
Let x=2, y=3.
Then the reciprocals of x and y are 1/2 and 1/3.
Since the reciprocal of r is equal to the sum of the reciprocals of x and y, we get:
1/r = 1/2 + 1/3
1/r = 3/6 + 2/6
1/r = 5/6
r = 6/5. This is our target.
Now we plug x=2 and y=3 into the answers to see which yields our target of 6/5.
Only answer choice
D works:
xy/(x+y) = (2*3)/(2+3) = 6/5.
The correct answer is
D.
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But can you explain for me more about reciprocals? I have no idea about this. Thanks so much!!!!
