Answer:
[tex]\tan{90^{\circ}}[/tex]
Step-by-step explanation:
Because [tex]\cos{x}[/tex] and [tex]\sin{x}[/tex] are defined for all [tex]x[/tex](i.e. their domain is [tex](-\infty, \infty)[/tex]), so they can never be undefined. However, [tex]\tan{90}=\sin{90}/\cos{90}=\sin{90}/0[/tex], which is undefined, because you can't divide by [tex]0[/tex]. So, the answer is [tex]\boxed{\tan{90^{\circ}}}[/tex]
