Solve lambda^2=(X-l)^2+4l^2

$$\lambda ^ { 2 } = ( X - l ) ^ { 2 } + 4 l ^ { 2 }$$

Solve for X (complex solution)

$$X=-\sqrt{\lambda ^{2}-4l^{2}}+l$$

$$X=\sqrt{\lambda ^{2}-4l^{2}}+l$$

Solve for l (complex solution)

$$l=\frac{-\sqrt{5\lambda ^{2}-4X^{2}}+X}{5}$$

$$l=\frac{\sqrt{5\lambda ^{2}-4X^{2}}+X}{5}$$

Solve for X

$$X=-\sqrt{\lambda ^{2}-4l^{2}}+l$$

$$X=\sqrt{\lambda ^{2}-4l^{2}}+l\text{, }|\lambda |\geq 2|l|$$

Solve for l

$$l=\frac{-\sqrt{5\lambda ^{2}-4X^{2}}+X}{5}$$

$$l=\frac{\sqrt{5\lambda ^{2}-4X^{2}}+X}{5}\text{, }|\lambda |\geq \frac{2\sqrt{5}|X|}{5}$$