# Quadratic, how to solve for R?

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

### 2 Answers

- 1 decade agoBest 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

- Anonymous1 decade ago
im pretty sure this isn't a quadratic equation.

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