Functions, graphs and inverses practice question 14

Find $\cos\theta$ from $\sin^{2}\theta + \cos^{2}\theta = 1$. Which sign does it take for an angle between $\dfrac{\pi}{2}$ and $\pi$?

$\cos^{2}\theta = \dfrac{45}{49}$, and cosine is negative in the second quadrant. Then $\tan\theta = \dfrac{\sin\theta}{\cos\theta}$.