Help simplify using quadratic formula

Question

$\dfrac{4\pm\sqrt{28}}{2}=2\pm\sqrt7$

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

Answer 1

Notice that $\sqrt{28}=\sqrt{4\times7}=\sqrt{4}\times\sqrt{7}=2\sqrt{7}$.

Hence $\dfrac{4\pm\sqrt{28}}{2}=\dfrac{4\pm2\sqrt{7}}{2}=\dfrac{2(2\pm\sqrt{7})}{2}=2\pm\sqrt{7}$.

Answer 2

$\dfrac{4\pm\sqrt{28}}{2}=$

$\dfrac{4\pm\sqrt{4\cdot7}}{2}=$

$\dfrac{4\pm\sqrt{4}\cdot\sqrt{7}}{2}=$

$\dfrac{4\pm2\cdot\sqrt{7}}{2}=$

$\dfrac{2\pm1\cdot\sqrt{7}}{1}=$

$2\pm\sqrt{7}$