\(\sqrt{a^2+a^2}\)

= \(\sqrt{2a^2}\)

= a\(\sqrt{2}\)

Giả sử \(1+a\ge b+c\)

Ta có \(1+a^3=b^3+c^3\)

\(\Leftrightarrow\left(1+a\right)\left(a^2-a+1\right)=\left(b+c\right)\left(b^2-bc+c^2\right)\)

\(\Leftrightarrow\frac{a^2-a+1}{b^2-bc+c^2}=\frac{b+c}{1+a}\le1\)

\(\Rightarrow a^2-a+1\le b^2-bc+c^2\)

\(\Leftrightarrow\left(a+1\right)^2-3a\le\left(b+c\right)^2-3bc\)(Vô lí vì giả sử a+1 > b+c và giả thiết a<bc)

Vậy điều giả sử là sai nên ta có dpcm

a) \(x+1=\sqrt{2\left(x+1\right)+2\sqrt{2\left(x+1\right)+2\sqrt{4\left(x+1\right)}}}\)

<=> \(\left(x+1\right)^2=\left[\sqrt{2\left(x+1\right)+2\sqrt{2\left(x+1\right)+2\sqrt{4\left(x+1\right)}}}\right]^2\)

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

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

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

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

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

<=> \(\left(x^2-1\right)^2=\left(2\sqrt{2x+2+4\sqrt{x+1}}\right)^2\)

<=> \(x^4-2x^2+1=8x+8+16\sqrt{x+1}\)

<=> \(x^4-2x^2+1-8x=16\sqrt{x+1}+8\)

<=> \(x^4-2x^2-8x-7=16\sqrt{x+1}\)

<=> \(\left(x^4-2x^2-8x-7\right)^2=\left(16\sqrt{x+1}\right)^2\)

<=> \(x^8-4x^6-16x^5-10x^4+32x^3+92x^2+112x+49=256x+256\)

<=> \(x^8-4x^6-16x^5-10x^4+32x^3+92x^2+112x-144x-207=0\)

<=> \(\left(x+1\right)\left(x-2\right)\left(x^6+2x^5+3x^4-4x^3-9x^2+2x+69\right)=0\)

<=> \(\orbr{\begin{cases}x+1=0\\x-3=0\end{cases}}\)<=> \(\orbr{\begin{cases}x=-1\\x=3\end{cases}}\)

Vì: \(x^6+2x^5+3x^4-4x^3-9x^2+2x+69\ne0\)

=> \(\orbr{\begin{cases}x=-1\\x=3\end{cases}}\)

1) \(\frac{1}{2}=\frac{1}{x}+\frac{1}{y}\ge\frac{4}{x+y}\)\(\Leftrightarrow\)\(x+y\ge8\)

\(\frac{1}{2}=\frac{1}{x}+\frac{1}{y}=\frac{x+y}{xy}\)\(\Leftrightarrow\)\(xy=2\left(x+y\right)\ge16\)

\(A=\sqrt{x}+\sqrt{y}\ge2\sqrt[4]{xy}\ge2\sqrt[4]{16}=4\)

Dấu "=" xảy ra \(\Leftrightarrow\)\(x=y=4\)

2) \(B=\sqrt{3x-5}+\sqrt{7-3x}\ge\sqrt{3x-5+7-3x}=\sqrt{2}\)

Dấu "=" xảy ra \(\Leftrightarrow\)\(\orbr{\begin{cases}x=\frac{5}{3}\\x=\frac{7}{3}\end{cases}}\)

\(B=\sqrt{3x-5}+\sqrt{7-3x}\le\frac{3x-5+1+7-3x+1}{2}=2\)

Dấu "=" xảy ra \(\Leftrightarrow\)\(x=2\)