# How do you simplify (sqrt19-sqrt2)^2 ?

You use the formula ${\left(a - b\right)}^{2} = {a}^{2} - 2 a b + {b}^{2}$
$= {\sqrt{19}}^{2} - 2 \cdot \sqrt{19} \cdot \sqrt{2} + {\sqrt{2}}^{2}$
$= 19 - 2 \sqrt{19 \cdot 2} + 2$
$= 21 - 2 \sqrt{38}$