\(\Leftrightarrow\hept{\begin{cases}y=2x-7\\x^2-2.x.\left(2x-7\right)=\left(7-2x\right).\left[9.\left(2x-7\right)+8x\right]\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}y=2x-7\\x^2-4x^2+14x=\left(7-2x\right).\left(26x-63\right)\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}y=2x-7\\-3x^2+14x=182x-441-52x^2+126x\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}y=2x-7\\49x^2-294x+441=0\end{cases}}\)\(\Leftrightarrow\hept{\begin{cases}y=2x-7\\49\left(x^2-6x+9\right)=0\end{cases}}\)\(\Leftrightarrow\hept{\begin{cases}y=2x-7\\\left(x-3\right)^2=0\end{cases}}\)\(\Leftrightarrow\hept{\begin{cases}x=3\\y=-1\end{cases}}\)

\(\hept{\begin{cases}x^2-2xy=-y\left(9y+8x\right)\\2x-y=7\end{cases}}\)(=) \(\hept{\begin{cases}x^2-2xy+9y^2+8xy=0\\2x-y=7\end{cases}}\)

(=)\(\hept{\begin{cases}x^2+6xy+9y^2-2xy+2xy=0\\2x-y=7\end{cases}}\)

(=)\(\hept{\begin{cases}\left(x+3y\right)^2=0\\2x-y=7\end{cases}}\) (=)\(\hept{\begin{cases}x+3y=0\\2x-y=7\end{cases}}\)(=)\(\hept{\begin{cases}2x+6y=0\left(1\right)\\2x-y=7\left(2\right)\end{cases}}\)

Trừ vế theo vế (2) cho (1) ta được :-7y=7 =>y=-1=>x=3. Vậy \(^{x^3+y^3^{ }=\left(-1\right)^3+3^3=26}\)

\(\Leftrightarrow\left(\sqrt{x+1}+\sqrt{x+16}\right)^2=\left(\sqrt{x+4}+\sqrt{x+9}\right)^2\)

\(\Leftrightarrow x+1+x+16+2.\sqrt{\left(x+1\right).\left(x+16\right)}=x+4+x+9+2.\sqrt{\left(x+4\right).\left(x+9\right)}\)

\(\Leftrightarrow2x+17+2.\sqrt{\left(x+1\right).\left(x+16\right)}=2x+13+2.\sqrt{\left(x+4\right).\left(x+9\right)}\)

\(\Leftrightarrow4+2.\sqrt{\left(x+1\right)\left(x+16\right)}=2.\sqrt{\left(x+4\right).\left(x+9\right)}\)

\(\Leftrightarrow2.\left(2+\sqrt{\left(x+1\right)\left(x+16\right)}\right)=2.\sqrt{\left(x+4\right).\left(x+9\right)}\)

\(\Leftrightarrow\sqrt{x^2+17x+16}+1=\sqrt{x^2+13x+36}\)

Bình phương 2 vế ta được 

\(x^2+17x+16+1+2.\sqrt{x^2+17x+16}=x^2+13x+36\)

\(\Leftrightarrow2.\sqrt{x^2+17x+16}=-4x+19\)

Bình phương 2 vế ta được 

\(2x^2+34x+32=16x^2-152x+361\)

\(\Leftrightarrow14x^2-186x+329=0\)

\(\Delta=\left(-186\right)^2-4.14.329=16172\)

\(x_1=\frac{186-\sqrt{16172}}{26}=2,262723898\)

\(x_2=\frac{186+\sqrt{16172}}{26}=12,04496841\)

\(\sqrt{x+1}+\sqrt{x+16}=\sqrt{x+4}+\sqrt{x+9}\) 

\(\left(\sqrt{x+1}+\sqrt{x+16}\right)^2=\left(\sqrt{x+4}+\sqrt{x+9}\right)^2\)  

\(x+1+x+16+2\sqrt{\left(x+1\right)\left(x+16\right)}=x+4+x+9+2\sqrt{\left(x+4\right)\left(x+9\right)}\)     

\(2x+17+2\sqrt{x^2+17x+16}=2x+13+2\sqrt{x^2+13x+36}\) 

\(4+2\sqrt{x^2+17x+16}=2\sqrt{x^2+13x+36}\)   

\(2+\sqrt{x^2+17x+16}=\sqrt{x^2+13x+36}\) 

\(\left(2+\sqrt{x^2+17x+16}\right)^2=\left(\sqrt{x^2+13x+36}\right)^2\)             

\(4+x^2+17x+16+4\sqrt{x^2+17x+16}=x^2+13x+36\) 

\(4\sqrt{x^2+17x+16}=-4x+16\) 

\(\sqrt{x^2+17x+16}=-x+4\)          

\(\hept{\begin{cases}-x+4\ge0\\x^2+17x+16=\left(-x+4\right)^2\end{cases}}\)    

\(\hept{\begin{cases}-x\ge-4\\x^2+17x+16=x^2-8x+16\end{cases}}\) 

\(\hept{\begin{cases}x\le4\\25x=0\end{cases}}\)  

\(\hept{\begin{cases}x\le4\\x=0\end{cases}}\)      

\(\Rightarrow x=0\) 

\(\Leftrightarrow\sqrt{x}+\sqrt{x+9}=\sqrt{x+1}+\sqrt{x+4}\)

\(\Leftrightarrow\left(\sqrt{x}+\sqrt{x+9}\right)^2=\left(\sqrt{x+1}+\sqrt{x+4}\right)^2\)

\(\Leftrightarrow x+x+9+2.\sqrt{x.\left(x+9\right)}=x+1+x+4+2.\sqrt{\left(x+1\right).\left(x+4\right)}\)

\(\Leftrightarrow2x+9+2.\sqrt{x^2+9x}=2x+5+2.\sqrt{x^2+5x+4}\)

\(\Leftrightarrow4+2.\sqrt{x^2+9x}=2.\sqrt{x^2+5x+4}\)

\(\Leftrightarrow2+\sqrt{x^2+9x}=\sqrt{x^2+5x+4}\)

\(\Leftrightarrow\left(2+\sqrt{x^2+9x}\right)^2=\left(\sqrt{x^2+5x+4}\right)^2\)

\(\Leftrightarrow2+x^2+9x+4.\sqrt{x^2+9x}=x^2+5x+4\)

\(\Leftrightarrow4.\sqrt{x^2+9x}=2-4x\)

\(\Leftrightarrow16.\left(x^2+9x\right)=\left(2-4x\right)^2\)

\(\Leftrightarrow16x^2+144x=16x^2-16x+4\)

\(\Leftrightarrow144x+16x=4\)

\(\Leftrightarrow160x=4\)

\(\Leftrightarrow x=\frac{1}{40}\)

ĐKXĐ: \(\orbr{\begin{cases}x\le-\frac{2}{\sqrt{5}}-1\\x\ge\frac{2}{\sqrt{5}}-1\end{cases}}\) 

PT \(\Leftrightarrow5\sqrt{5x^2+10x+1}=35-10x-5x^2\) 

\(\Leftrightarrow5\sqrt{5x^2+10x+1}=36-\left(5x^2+10x+1\right)\) 

Đặt \(\sqrt{5x^2+10x+1}=y\ge0\) 

\(\Rightarrow y^2+5y-36=0\) 

\(\Rightarrow\orbr{\begin{cases}y=4\\y=-9\end{cases}}\) 

Tự tìm x

\(Ca\left(OH\right)_2+SO_2\rightarrow CaSO_3+H_2O\)

    5mol               5mol       5mol           5mol

\(n_{SO_2}=\frac{V}{22,4}=\frac{112}{22,4}=5mol\)

\(m_{CaSO_3}=n.M=5.120=600g\)

Cái này phải mua bạn nhé, xem tại đây http://www.davibooks.vn/products/view/42824.Tai-Lieu-Chuyen-Toan-Trung-Hoc-Co-So-Toan-9-Tap-1-dai-So.html

Mk chưa mua được nhưng cần gấp

\(B=\frac{-2a\sqrt{a}+2a^2}{\left(\sqrt{a}-\right)\left(a-1\right)}\)

\(C=-x\sqrt{x}+x+\sqrt{x}-1\)

\(D=x-\sqrt{x}+1\)

có đáp án kĩ hơn không ạ ?

\(A=\frac{x-\sqrt{x}+1}{\sqrt{x}}\)