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math-calculus

posted by on .

the formula 1/R = 1/R1 + 1/R2, concerning resistance in an electrical circuit is used in physics. if R = 3 ohms and R1 is 8 ohms more than R2, the value of R1 be?

this also not make any sense to me

  • math-calculus - ,

    R2 = R1 - 8
    R1 R2 = R R2 + R R1 = R(R1+R2)

    R1(R1-8) = 3(2 R1 - 8)

    R1^2 - 8 R1 = 6 R1 - 24

    R1^2 -14 R1 + 24 = 0

    (R1-12)(R1-2) = 0
    If R1 were 2, R2 would be negative, no good
    so
    R1 = 12 (and R2 is 4)

  • math-calculus - ,

    that make sense now :) thanks very much damon :)

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