Step-by-step explanation:
[tex]\sqrt{a}=b\iff b^2=a,\ \text{for}\ a\geq0\ \text{and}\ b\geq0.\\\\a.\ \sqrt{16}=4\ \text{because}\ 4^2=16\\\\b.\ \sqrt{169}=13\ \text{because}\ 13^2=169\\\\c.\ \sqrt{64}=8\ \text{because}\ 8^2=64\\\\d.\ \sqrt{400}=20\ \text{because}\ 20^2=400[/tex]
