Chapter 13, Trigonometric Ratios and Functions - 13.3 Evaluate Trigonometric Functions of Any Angle - 13.3 Exercises - Skill Practice - Page 871: 12

$\sin 0^{\circ}=0$ $\cos 0^{\circ}=1$ $\tan 0^{\circ}=0$ $\csc 0^{\circ}= \infty$ $\sec 0^{\circ}=1$ $\cot 0^{\circ}=\infty $

When $\theta= 0^{\circ}$ The Trigonometric Identities can be defined as: $\sin 0^{\circ}=0$ $\cos 0^{\circ}=1$ $\tan 0^{\circ}=0$ $\csc 0^{\circ}= \infty$ $\sec 0^{\circ}=1$ $\cot 0^{\circ}=\infty $