Solve for R?(Math)???????

1/r - r/2 = 3/5

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  • KevinM
    Lv 7
    1 decade ago
    Favorite Answer

    Multiply by r:

    1 - 1/2 r^2 = 3/5 r

    1/2 r^2 + 3/5 r - 1 = 0

    5 r^2 + 6r - 10 = 0

    And solve using the quadratic equation.

  • 1 decade ago

    First, get the left side into one fraction...that means getting a common denominator.

    Because the denominators are r and 2, the common denominator is 2r.

    Then, rewrite the fractions on the left with the new denominator:

    (1/r)*(2/2) - (r/2)*(r/r) = 3/5

    --> (2/2r) - (r^2/2r) = 3/5

    --> (2 - r^2)/2r = 3/5

    Cross multiply...

    --> 5(2 - r^2) = 3*2r

    --> 10 - 5r^2 = 6r

    --> 5r^2 + 6r - 10 = 0

    Use the quadratic formula to solve for r:

    r = (-6 +- sqrt(36 +4*5*10)) / (2*5)

    r = (-6 +- sqrt(236)) / 10

    Simplifying, you get the set of two solutions....

    r = { (-3 - sqrt(59)) / 5, (-3 + sqrt(59)) / 5 }

  • 1 decade ago

    1/r - r/2 = 3/5

    *(10R) then

    10 - 5r^2 = 6r

    0= 5r^2 + 6r -10

    here we have to use normal eq ax^2 + bx + c = 0

    then you can get the answer.

    here a= 5 ; b=6 ; c=-10

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