a)\(\sqrt{\left(2-\sqrt{5}\right)^2}-\left(\sqrt{5+2}\right)\)
b)\(x-5\sqrt{x}+4=0\)
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9x+2=y^2+y<=>9x+2=y(y+1)
VT chia 3 dư 2 nên VP cũng chia 3 dư 2
=>y=3k+1 và y+1=3k+2 ( k nguyên)
khi đó 9x+2=(3k+1)(3k+2)
<=>9x=9k^2+9k <=>x=k^2+k<=>x=k(k+1)
Vậy pt có nghiệm nguyên (x;y) là (k(k+1));(3k+1)
Ta có : P = \(1-3x+\frac{3}{2-x}=6-3x+\frac{3}{2-x}\) \(-5\) \(=3\left(2-x\right)+\frac{3}{2-x}-5\)
Áp dụng BĐT : AM-GM ta được :
\(3\left(2-x\right)+\frac{3}{2-x}\ge2\sqrt{\frac{3\left(2-x\right)3}{\left(2-x\right)}}=\)\(2\sqrt{9}=2.3=6\)
Vì x<2 => dấu "=" xảy ra khi : x=1
=> P \(\ge6-5=1\)
Vậy Min P = 1 khi x=1
\(\frac{x^2-5}{3x}-\frac{2}{3}=\frac{x^2-2x-5}{3x}=\frac{\left(x-1+\sqrt{6}\right)\left(x-1-\sqrt{6}\right)}{3x}\)
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