8 - 2 15 is equal to = ?

Answer: Option B

$$\begin{array}{rl}& \sqrt{8-2\sqrt{15}}\\ & =\sqrt{5+3-2\times \sqrt{5}\times \sqrt{3}}\\ & =\sqrt{{\left(\sqrt{5}\right)}^2+{\left(\sqrt{3}\right)}^2-2\times \sqrt{5}\times \sqrt{3}}\\ & =\sqrt{{\left(\sqrt{5}-\sqrt{3}\right)}^2}\\ & =\left(\sqrt{5}-\sqrt{3}\right)\end{array}$$