SOLUTION: Two resistors,when connected in series,have a total resistance of 40 ohms.When connected in parallel their total resistance is 8.4 ohms.If one of the resistors has a resistance of

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Question 40557: Two resistors,when connected in series,have a total resistance of 40 ohms.When connected in parallel their total resistance is 8.4 ohms.If one of the resistors has a resistance of Rx ohms:
(a) show that Rx^2-40Rx+336=0
&
(b)calculate the resistance of each.
answers ( 12 ohms,28 ohms)
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
R%281%29+%2B+R%282%29+=+40
1%2FR%281%29+%2B+1%2FR%282%29+=+1%2F8.4
R%5E2+-40R+%2B+336+=+0
R+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
R+=+%2840+%2B-+sqrt%28+%28-40%29%5E2-4%2A1%2A336+%29%29%2F%282%2A1%29+
R+=+%2840+%2B-+sqrt%28+1600+-+1344+%29%29%2F+2+
R+=+%2840+%2B-+sqrt%28+256+%29%29%2F+2+
R+=+20+%2B+8
R+=+20+-+8
R = 28,12
check these values
R%281%29+%2B+R%282%29+=+40
1%2FR%281%29+%2B+1%2FR%282%29+=+1%2F8.4
28+%2B+12+=+40
OK
1%2F28+%2B+1%2F12+=+1%2F8.4
multiply both sides by 4
1%2F7+%2B+1%2F3+=+1%2F2.1
multiply both sides by 21
3+%2B+7+=+10
OK