Question

Giúp mik câu 3 bài 1 với ạ

Answer 1

1: Khi x=9 thì \(A=\dfrac{9+2+4}{3-2}=15\)

2: \(B=\dfrac{3x-4-x+4-x+\sqrt{x}}{\sqrt{x}\left(\sqrt{x}-2\right)}\)

\(=\dfrac{x+\sqrt{x}}{\sqrt{x}\left(\sqrt{x}-2\right)}=\dfrac{\sqrt{x}+1}{\sqrt{x}-2}\)

3: \(P=\dfrac{A}{B}=\dfrac{x+\sqrt{x}+4}{\sqrt{x}-2}:\dfrac{\sqrt{x}+1}{\sqrt{x}-2}\)

\(=\dfrac{x+\sqrt{x}+4}{\sqrt{x}+1}=\sqrt{x}+\dfrac{4}{\sqrt{x}+1}\)

\(=\sqrt{x}+1+\dfrac{4}{\sqrt{x}+1}-1\)

=>\(P>=2\sqrt{\left(\sqrt{x}+1\right)\cdot\dfrac{4}{\sqrt{x}+1}}-1=2\cdot2-1=3\)

Dấu = xảy ra khi (căn x+1)^2=4

=>căn x+1=2

=>x=1