## Trigonometry 7th Edition

The calculator displays an error message. This is because ratio cotangent is not defined for angle $0^{\circ}$.
In degree mode, the calculator on pressing $0$ first and then $tan$, displays an error message. Let's try finding value of $\cot 0^{\circ}$ by an alternate method- $\cot 0^{\circ}$ = $\frac{\cos 0^{\circ}}{\sin 0^{\circ}}$ (ratio identity) Now from table, substituting the values of $\cos 0^{\circ}$ and $\sin 0^{\circ}$- $\cot 0^{\circ}$ = $\frac{1}{0}$ Thus $\cot 0^{\circ}$ becomes undefined because division by zero is not defined. Calculators are also programmed accordingly.