Quadratic, how to solve for R?

22.4 = (120/R+139)^2 * R

2 Answers

  • 1 decade ago
    Favorite Answer

    Simplify: (square the top and bottom of the fraction, then multiply top by R:

    22.4 = 14400R/(R+139)^2

    Clear fraction: (multiply both sides by (R+139)^2)

    22.4(R+139)^2 = 14400R

    Like terms/simplify: (divide both sides by 22.4 first, then subtract the result on the right onto the left side. Meanwhile, expand your squared stuff)

    (R+139)^2 = 14400R/22.4

    R^2 + 278R + 19321 = 642.857R

    R^2 - 364.857R + 19321 = 0

    Plug this equation into your graphing calculator as y=x^2 - 364.857x + 19321 in a good viewing window and then find the zeroes. The x-values = R.

    Answer: R = 64.280, 300.577

    Plug these back into your equation, and they both equal approximately 22.4

  • Anonymous
    1 decade ago

    im pretty sure this isn't a quadratic equation.

    a quadratic equation has the format z^2*bx+c

Still have questions? Get your answers by asking now.