\(A=\left(\frac{\sqrt{x}}{\sqrt{x}-2}-\frac{x-3}{x+2\sqrt{x}+4}-\frac{7\sqrt{x}+10}{x\sqrt{x}-8}\right):\left(\frac{\sqrt{x}+7}{x+2\sqrt{x}+4}\right)\)
\(=\left(\frac{\sqrt{x}}{\sqrt{x}-2}-\frac{x-3}{x+2\sqrt{x}+4}-\frac{7\sqrt{x}+10}{\sqrt{x}^3-8}\right):\left(\frac{\sqrt{x}+7}{x+2\sqrt{x}+4}\right)\)
\(=\left(\frac{\sqrt{x}\left(x+2\sqrt{x}+4\right)}{\sqrt{x}^3-8}-\frac{\left(x-3\right)\left(\sqrt{x}-2\right)}{\sqrt{x}^3-8}-\frac{7\sqrt{x}+10}{\sqrt{x}^3-8}\right)\)\(:\left(\frac{\sqrt{x}+7}{x+2\sqrt{x}+4}\right)\)
\(=\frac{\sqrt{x}^3+2x+4\sqrt{x}-\sqrt{x}^3+2x+3\sqrt{x}-6-7\sqrt{x}-10}{\left(\sqrt{x}-2\right)\left(x+2\sqrt{x}+4\right)}.\frac{\left(x+2\sqrt{x}+4\right)}{\sqrt{x}+7}\)
\(=\)\(\frac{\left(4x-16\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+7\right)}=\frac{4\left(x-4\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+7\right)}\)
Sai đề không ?
A= \(\left(\frac{\sqrt{x}\left(x+2\sqrt{x}+4\right)-\left(x-3\right)\left(\sqrt{x}-2\right)-7\sqrt{x}+10}{\left(\sqrt{x}-2\right)\left(x+2\sqrt{x}+4\right)}\right)\) . \(\frac{x+2\sqrt{x}+4}{\sqrt{x}+7}\)
= \(\frac{x\sqrt{x}+2x+4\sqrt{x}-x\sqrt{x}+3\sqrt{x}-6+2x-7\sqrt{x}-10}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+7\right)}\)
= \(\frac{4x-16}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+7\right)}\)
=\(\frac{4\left(x-4\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+7\right)}\)
= \(\frac{4\left(\sqrt{x}+2\right)}{\sqrt{x}+7}\)
= \(\frac{4\sqrt{x}+8}{\sqrt{x}+7}\)
#mã mã#
Cám ơn bạn mã mã , để mình làm nốt nhé :
\(A=\frac{4\sqrt{x}+8}{\sqrt{x}+7}\)
Để \(A>2\Rightarrow\frac{4\sqrt{x}+8}{\sqrt{x}+7}>2\)
\(\Rightarrow\frac{4\sqrt{x}+8}{\sqrt{x}+7}-2>0\)
\(\Rightarrow\frac{4\sqrt{x}+8-2\sqrt{x}-14}{\sqrt{x}+7}>0\)
\(\Rightarrow\frac{2\sqrt{x}-6}{\sqrt{x}+7}>0\)
Vì \(\sqrt{x}>0\Rightarrow\sqrt{x}+7>0\)\(\Rightarrow A>0\Leftrightarrow2\sqrt{x}-6>0\)
\(\Rightarrow2\left(\sqrt{x}-3\right)>0\Rightarrow\sqrt{x}-3>0\)
\(\Leftrightarrow\sqrt{x}>3\Rightarrow\sqrt{x}>\sqrt{9}\Rightarrow x>9\)
Vậy để \(A>2\Leftrightarrow x>9\)
Phạm thị hùy linh làm như cậu là đúng nhưng cậu bị sai đề bài A <2
chỗ rút gọn mk thiếu đk x\(\ge\)0 , x \(\ne\) 4
để A <2 hay \(\frac{4\sqrt{x}+8}{\sqrt{x}+7}\)<2
\(\Rightarrow\)\(4\sqrt{x}\)+ 8 < 2\(\sqrt{x}\)+14
(vì mẫu >0 nên mk có thể nhân chéo đc )
\(\Leftrightarrow\)\(2\sqrt{x}\)< 6
\(\Leftrightarrow\)\(\sqrt{x}< 3\)
\(\Leftrightarrow\)x<9
Mà x \(\ge\)0 , x\(\ne\)4 \(\Rightarrow\)0 \(\le\)x<9 , x \(\ne\)4
vậy để A<2 thì 0 \(\le\)x < 9 , x\(\ne\)4
#mã mã#