Số bài dự thi trung bình moi64 ngày ban tổ chức nhận là : 

\(1308:12=109\) (bài)

D/S: 109 bài

\(54+\left(98-x\right)=73\\ \Rightarrow98-x=19\\ \Rightarrow x=79\)

\(a,3\sqrt{x}-7=0\left(dk:x\ge0\right)\\ \Leftrightarrow3\sqrt{x}=7\\ \Leftrightarrow\sqrt{x}=\dfrac{7}{3}\\ \Leftrightarrow x=\dfrac{49}{9}\left(tmdk\right)\)

Vậy \(S=\left\{\dfrac{49}{9}\right\}\)

\(b,\sqrt{x-2}+\sqrt{4x-8}=3\left(dk:x\ge2\right)\\ \Leftrightarrow\sqrt{x-2}+\sqrt{4\left(x-2\right)}=3\\ \Leftrightarrow\sqrt{x-2}+2\sqrt{x-2}=3\\ \Leftrightarrow3\sqrt{x-2}=3\\ \Leftrightarrow\sqrt{x-2}=1\\ \Leftrightarrow x-2=1\\ \Leftrightarrow x=3\left(tmdk\right)\)

Vậy \(S=\left\{3\right\}\)

\(a,\sqrt{4u-20}+3\sqrt{\dfrac{u-5}{9}}-\dfrac{1}{3}\sqrt{9u-45}=4\left(dk:u\ge5\right)\)

\(\Leftrightarrow2\sqrt{u-5}+3.\dfrac{\sqrt{u-5}}{3}-\dfrac{1}{3}.3\sqrt{u-5}=4\\ \Leftrightarrow2\sqrt{u-5}+\sqrt{u-5}-\sqrt{u-5}=4\\ \Leftrightarrow\sqrt{u-5}\left(2+1-1\right)=4\\ \Leftrightarrow\sqrt{u-5}=2\\ \Leftrightarrow u-5=4\\ \Leftrightarrow u=9\left(tm\right)\)

Vậy \(S=\left\{9\right\}\)

\(b,\dfrac{2}{3}\sqrt{9u-9}-\dfrac{1}{4}\sqrt{16u-16}+27\sqrt{\dfrac{u-1}{81}}=4\left(dk:u\ge1\right)\)

\(\Leftrightarrow2\sqrt{u-1}-\sqrt{u-1}+3\sqrt{u-1}=4\\ \Leftrightarrow\sqrt{u-1}.\left(2-1+3\right)=4\\ \Leftrightarrow\sqrt{u-1}=1\\ \Leftrightarrow u-1=1\\ \Leftrightarrow u=2\left(tm\right)\)

Vậy \(S=\left\{2\right\}\)

\(a,\left|-4x\right|=x+2\\ TH_1:x\le0\\ -4x=x+2\Leftrightarrow-4x-x=2\Leftrightarrow-5x=2\Leftrightarrow x=-\dfrac{2}{5}\left(tm\right)\\ TH_2:x>0\\ 4x=x+2\Leftrightarrow3x=2\Leftrightarrow x=\dfrac{2}{3}\left(tm\right)\)

Vậy \(S=\left\{-\dfrac{2}{5};\dfrac{2}{3}\right\}\)

\(b,\left|2-x\right|=2-3x\\ TH_1:x\le2\\ 2-x=2-3x\Leftrightarrow2x=0\Leftrightarrow x=0\left(tm\right)\\ TH_2:x>2\\ -2+x=2-3x\Leftrightarrow4x=4\Leftrightarrow x=1\left(ktm\right)\)

Vậy \(S=\left\{0\right\}\)

\(c,\left|2x-3\right|=5x-6\\ TH_1:x\ge\dfrac{3}{2}\\ 2x-3=5x-6\Leftrightarrow-3x=-3\Leftrightarrow x=1\left(ktm\right)\\ TH_2:x< \dfrac{3}{2}\\ -2x+3=5x-6\Leftrightarrow-7x=-9\Leftrightarrow x=\dfrac{9}{7}\left(tm\right)\)

Vậy \(S=\left\{\dfrac{9}{7}\right\}\)

 rồi á anh ơi,phong thanh cùng nghĩa với phong phanh có nghĩa là nghe thoáng qua á 

\(=\left(\dfrac{\sqrt{x}\left(\sqrt{x}+3\right)+6+2\sqrt{x}}{\sqrt{x}+3}\right)\left(\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)}{\sqrt{x}-1}-\dfrac{2\left(\sqrt{x}+1\right)}{\sqrt{x}+1}\right)\\ =\dfrac{x+3\sqrt{x}+6+2\sqrt{x}}{\sqrt{x}+3}.\left(\sqrt{x}-2\right)\\ =\dfrac{\sqrt{x}\left(\sqrt{x}+3\right)+2\left(3+\sqrt{x}\right)}{\sqrt{x}+3}.\left(\sqrt{x}-2\right)\\ =\dfrac{\left(\sqrt{x}+2\right)\left(\sqrt{x}+3\right)}{\sqrt{x}+3}.\left(\sqrt{x}-2\right)\\ =\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)\\ =x-4\)