Resposta :
[tex]\Large\boxed{\begin{array}{l}\sf B=(\sqrt{5}+\sqrt{3})\cdot(\sqrt{5}-\sqrt{3})\\\sf B=(\sqrt{5})^2-(\sqrt{3})^2\\\sf B=5-3\\\sf B=2\\\huge\boxed{\boxed{\boxed{\boxed{\sf\maltese~alternativa~a}}}}\end{array}}[/tex]
[tex]\Large\boxed{\begin{array}{l}\sf B=(\sqrt{5}+\sqrt{3})\cdot(\sqrt{5}-\sqrt{3})\\\sf B=(\sqrt{5})^2-(\sqrt{3})^2\\\sf B=5-3\\\sf B=2\\\huge\boxed{\boxed{\boxed{\boxed{\sf\maltese~alternativa~a}}}}\end{array}}[/tex]