Cosine and secant are reciprocals, as they should be. You can draw a right triangle with side adjacent angle Y having length 8 and hypotenuse having length 17. Using the Pythagorean Theorem, you will find that the side opposite to angle Y is 15. It follows that: $\displaystyle{\cot{{Y}}}=\frac{{a}}{{o}}=\frac{{8}}{{15}}\usepackage{cmbright}\Huge\$