This expression simplifies to:

(cos(105) - cos(15)) / cos(315)

Using trigonometric identities, we can expand the cosine values:

(cos(105) - cos(15)) / cos(315)
= (cos(60 + 45) - cos(15)) / cos(315)
= (cos(60)cos(45) - sin(60)sin(45) - cos(15)) / cos(315)
= ((1/2)(√2/2) - (√3/2)(√2/2) - cos(15)) / cos(315)
= (√2/4 - √6/4 - cos(15)) / cos(315)

Therefore, the expression is (√2/4 - √6/4 - cos(15)) / cos(315)