Tangent and cotangent are reciprocals, as they should be. You can draw a right triangle with side opposite angle Y having length 3 and with side adjacent angle Y having length 4. Using the Pythagorean Theorem, you will find that the hypotenuse is 5. It follows that: $\displaystyle{\sin{{Y}}}=\frac{{o}}{{h}}=\frac{{3}}{{5}}\usepackage{cmbright}\Huge\$