## Calculus (3rd Edition)

$\cos\theta= - \frac{\sqrt {21}}{5}$ and $\tan\theta=-\frac{2\sqrt {21}}{21}$
$\sin\theta=0.4=\frac{2}{5}$ $\cos^{2}\theta=1-\sin^{2}\theta=1-\frac{4}{25}=\frac{21}{25}$ $\cos\theta=± \frac{\sqrt {21}}{5}$ Since $\theta$ lies in second quadrant, $\cos\theta$ is negative. Therefore $\cos\theta= - \frac{\sqrt {21}}{5}$ $\tan\theta=\frac{\sin\theta}{\cos\theta}=\frac{\frac{2}{5}}{ - \frac{\sqrt {21}}{5}}=-\frac{2}{\sqrt {21}}=-\frac{2\sqrt {21}}{21}$