How to further simplify?

Question

[1 - cos∅/√(n²-sin²∅)]where n is constant and ∅ is very small angle.

Answer 1

You appear to have 1 - (cos ∅/√(n²-sin²∅) which, for very small angle, we can approximate as
1 - 1/√(n²-sin²∅) or 1 - 1/√(n²) which is 1- 1/|n|

My answer is ONE, minus the reciprocal of the absolute value of n. This is based on the ABSENCE OF any parentheses prior to the one division symbol in your expression.