$A=60^{\circ}, B=45^{\circ}$ হলে, $\cos (B-A)$ এর মান কোনটি ?

$\frac{2 \sqrt{2}}{\sqrt{3}-1}$

$\frac{2 \sqrt{2}}{\sqrt{3}+1}$

$\frac{\sqrt{3}+1}{2 \sqrt{2}}$

$\frac{\sqrt{3}-1}{2 \sqrt{2}}$