# What is the distance between  (–5, –9)  and  (–4, 7) ?

$\sqrt{257}$
You first form the vector between those points : $\left(- 4 - \left(- 5\right) , 7 - \left(- 9\right)\right) = \left(1 , 16\right)$. You then calculate its norm by the formula $\sqrt{{x}^{2} + {y}^{2}}$
$\sqrt{1 + {16}^{2}} = \sqrt{257}$