Leysa x=22000/(1+r)^2-18000

$$x = \frac { 22000 } { ( 1 + r ) ^ { 2 } } - 18000$$

Leystu fyrir r (complex solution)

$$r=\frac{\sqrt{55}\left(-x-18000\right)^{-\frac{1}{2}}\left(-\sqrt{55\left(-x-18000\right)}-1100i\right)}{55}$$

$$r=\frac{\sqrt{55}\left(-x-18000\right)^{-\frac{1}{2}}\left(-\sqrt{55\left(-x-18000\right)}+1100i\right)}{55}\text{, }x\neq -18000$$

Leystu fyrir r

$$r=\frac{\sqrt{\frac{55}{x+18000}}\left(-\sqrt{55\left(x+18000\right)}+1100\right)}{55}$$

$$r=\frac{\sqrt{\frac{55}{x+18000}}\left(-\sqrt{55\left(x+18000\right)}-1100\right)}{55}\text{, }x>-18000$$

Leystu fyrir x

$$x=-\frac{2000\left(9r^{2}+18r-2\right)}{\left(r+1\right)^{2}}$$

$$r\neq -1$$