The cotangent is correct, but it looks like you found $\displaystyle{\cos{{D}}}\usepackage{cmbright}\Huge\$ instead of $\displaystyle{\cos{{C}}}\usepackage{cmbright}\Huge\$ .

C and D are complementary angles, so their cofunctions are equal:

$\displaystyle{\cot{{D}}}={\tan{{C}}}\usepackage{cmbright}\Huge\$ and $\displaystyle{\cos{{C}}}={\sin{{D}}}\usepackage{cmbright}\Huge\$