## Trigonometry 7th Edition

$\sin{180^o} = 0 \\\cos{180^o} = -1 \\\tan{180^o} = 0 \\\cot{180^o} \text{ is undefined} \\\csc{180^o} \text{ is undefined} \\\sec{180^o} = -1$
RECALL: If $P(x, y)$ is on a unit circle, then $\begin{array}{cc} &\cos{\theta} = x &\sec{\theta} = \frac{1}{x}, x\ne 0 \\&\sin{\theta} = y &\csc{\theta} = \frac{1}{y}, y\ne 0 \\&\tan{\theta} = \frac{y}{x}, x\ne 0 &\cot{\theta} = \frac{x}{y}, y \ne 0 \end{array}$ Refer to the unit circle on page 137 of this textbook. Thus, using the ratios in the recall part above, and with $P(-1, 0)$, gives: $\sin{180^o} = 0 \\\cos{180^o} = -1 \\\tan{180^o} = \dfrac{0}{-1} =0 \\\cot{180^o}=\dfrac{-1}{0} \text{( undefined)} \\\csc{180^o}=\dfrac{1}{0} \text{( undefined)} \\\sec{180^o} = \frac{1}{-1}=-1$