## Precalculus (6th Edition)

$\color{blue}{\cos{\frac{7\pi}{4}}=\dfrac{\sqrt2}{2}}$
RECALL: (i) $\cos{s} = x$ (ii) $\sin{s} = y$ (iii) $\tan{s}=\dfrac{y}{x}$ (iv) $\sec{s} =\dfrac{1}{x}$ (v) $\csc{s} = \dfrac{1}{y}$ (vi) $\cot{s} = \dfrac{x}{y}$ Use the coordinates of the unit circle point above and the formula in (i) above to obtain: $\color{blue}{\cos{\frac{7\pi}{4}}=\dfrac{\sqrt2}{2}}$