Help simplify using quadratic formula $\dfrac{4\pm\sqrt{28}}{2}=2\pm\sqrt7$
My Question is how did $\dfrac{4\pm\sqrt{28}}{2}$ become simplified as $2\pm\sqrt7$
Can you help me by explaining the steps clearly 
:) Many Thanks

$\dfrac{4\pm\sqrt{28}}{2}=$
$\dfrac{4\pm\sqrt{4\cdot7}}{2}=$
$\dfrac{4\pm\sqrt{4}\cdot\sqrt{7}}{2}=$
$\dfrac{4\pm2\cdot\sqrt{7}}{2}=$
$\dfrac{2\pm1\cdot\sqrt{7}}{1}=$
$2\pm\sqrt{7}$
