số lớn nhất có 2 cs là 99 thì a+b=9+9=18

số bé nhất có 2 cs là -99 thì a+b=(-9)+(-9)=-18

\(\sqrt{121}-2\sqrt{16}=11-2.4=11-8=3\)

\(\sqrt{61^2-60^2}=\sqrt{\left(61-60\right).\left(61+60\right)}=\sqrt{1.121}=11\)\(\sqrt{\left(\sqrt{5}-2\right)^2}=\sqrt{5}-2\)

\(2\sqrt{32}+\sqrt{98}-3\sqrt{18}=8\sqrt{2}+7\sqrt{2}-9\sqrt{2}=6\sqrt{2}\)

\(M=x-\sqrt{x}=\left(\sqrt{x}-\dfrac{1}{2}\right)^2-\dfrac{1}{4}\)

ta co \(\left(\sqrt{x}-\dfrac{1}{2}\right)^2\ge0\) voi moi x

suy ra \(\left(\sqrt{x}-\dfrac{1}{2}\right)^2-\dfrac{1}{4}\ge-\dfrac{1}{4}\)

vay gia tri min cua M la\(-\dfrac{1}{4}\)

\(a^3+b^3=\left(a+b\right)\left(a^2-ab+b^2\right)=\left(a+b\right)\left(\left(a+b\right)^2-3ab\right)=\left(a+b\right)^3-\left(a+b\right).3ab=\left(\sqrt{3}\right)^3-\sqrt{3}.3\sqrt{2}=3\sqrt{3}-3\sqrt{6}\)

a) \(\sqrt{\dfrac{27a^2}{48a^4}}=\sqrt{\dfrac{9}{16a^2}}=\dfrac{3}{4a}\)

b) \(\dfrac{\sqrt{9x^2-25}}{\sqrt{3x+5}}=2\Leftrightarrow\dfrac{\sqrt{\left(3x-5\right)\left(3x+5\right)}}{\sqrt{3x+5}}=2\Leftrightarrow\sqrt{3x-5}=2\Leftrightarrow3x-5=4\Leftrightarrow x=3\)c) \(\sqrt{3-\sqrt{5}}+\sqrt{3+\sqrt{5}}=\dfrac{\sqrt{2}\left(\sqrt{3-\sqrt{5}}+\sqrt{3+\sqrt{5}}\right)}{\sqrt{2}}=\dfrac{\sqrt{6-2\sqrt{5}}+\sqrt{6+2\sqrt{5}}}{\sqrt{2}}=\dfrac{\sqrt{5}-1+\sqrt{5}+1}{\sqrt{2}}=\dfrac{2\sqrt{5}}{\sqrt{2}}=\sqrt{10}\)d) \(\dfrac{a\sqrt{a}+b\sqrt{b}-a\sqrt{b}-b\sqrt{a}}{a+b-2\sqrt{ab}}=\dfrac{a\left(\sqrt{a}-\sqrt{b}\right)-b\left(\sqrt{a}-\sqrt{b}\right)}{\left(\sqrt{a}-\sqrt{b}\right)^2}=\dfrac{\left(a-b\right)\left(\sqrt{a}-\sqrt{b}\right)}{\left(\sqrt{a}-\sqrt{b}\right)^2}=\sqrt{a}+\sqrt{b}\)

\(A=\left[\dfrac{\sqrt{a}\left(\sqrt{a}-1\right)}{\sqrt{a}-1}+1\right].\left[\dfrac{\sqrt{a}\left(\sqrt{a}+1\right)}{\sqrt{a}+1}-1\right]\)\(A=\left(\sqrt{a}+1\right).\left(\sqrt{a}-1\right)\)

\(A=a-1\)

b) \(A>3\Leftrightarrow a-1>3\Leftrightarrow a>4\)

Diện tích phần làm nhà là:60m²

Choose the best answer:

It’s very difficult……….all these things.

A. remembered

B. remembering

C. remember

D. to remember