Tất cả đều bằng nhau.

a: \(\dfrac{\sqrt{81}}{\sqrt{16}}=\dfrac{9}{4}=\dfrac{36}{16}< \dfrac{81}{16}\)

b: \(\sqrt{16+25}=\sqrt{41}< 9=\sqrt{16}+\sqrt{25}\)

Lời giải:
$\sqrt{0,16}+\sqrt{\frac{4}{25}}=\sqrt{0,16}+\sqrt{0,16}$

$=2\sqrt{0,16}=2\sqrt{0,4^2}=2.0,4=0,8$

\(\sqrt{0.16}+\sqrt{\dfrac{4}{25}}\)

\(=0.4+\dfrac{2}{5}\)

=0.8

\(\sqrt{16}=4\)

\(\sqrt{49}=7\)

\(\sqrt{121}=11\)

\(\sqrt{169}=13\)

\(\sqrt{196}=14\)

trả lời 

\(\sqrt{16}\);\(\sqrt{49}\);\(\sqrt{121}\);\(\sqrt{169}\);\(\sqrt{196}\)

chúc bn hok tốt 

Cảm ơn bạn

\(5\sqrt{16}-4\sqrt{9}+\sqrt{25}-0,3\sqrt{400}\)

\(=20-12+5-6\)

\(=7\)

Ý của bạn là \(\left(5\sqrt{16}\right)-\left(4\sqrt{9}\right)+\left(\sqrt{25}\right)-\left(0,3\sqrt{400}\right)\)phải k???

\(\left(5\sqrt{16}\right)-\left(4\sqrt{9}\right)+\left(\sqrt{25}\right)-\left(0,3\sqrt{400}\right)\)

\(=\left(5.4\right)-\left(4.3\right)+5-\left(0,3.20\right)\\ =20-12+5-6\\ =8+5-6\\ =13-6\\ =7\)

Chúc các bạn học tốt

\(4-\sqrt{x^2+1}-2\sqrt{16\left(x^2+1\right)}+5\sqrt{25\left(x^2+1\right)}\)

\(=4-\sqrt{x^2+1}-4\sqrt{x^2+1}+25\sqrt{x^2+1}\)

\(=20\sqrt{x^2+1}+4\)

\(\sqrt{16}\)=4

\(\sqrt{49}\)=7