$\sqrt{289}=17;-\sqrt{144}=-12;\sqrt{\frac{81}{225}}=\frac{9}{15}=\frac{3}{5};\sqrt{(-3)^{2}}=3;\sqrt{a^{2}}=\left | a\right |$
Bài 4. Hãy tính: $\sqrt{289};-\sqrt{144};\sqrt{\frac{81}{225}};\sqrt{(-3)^{2}};\sqrt{a^{2}}$
$\sqrt{289}=17;-\sqrt{144}=-12;\sqrt{\frac{81}{225}}=\frac{9}{15}=\frac{3}{5};\sqrt{(-3)^{2}}=3;\sqrt{a^{2}}=\left | a\right |$