\(a,=\dfrac{9}{5}+\dfrac{4}{15}=\dfrac{27}{15}+\dfrac{4}{15}=\dfrac{31}{15}\\ b,=\dfrac{3}{4}-\dfrac{2}{7}=\dfrac{13}{28}\)

mặt lé ấy mak -.- 

\(a,x-4,03=5,94\\ x=5,94+4,03\\ x=9,97\)

________________

\(b,13,7+x=59,8\\ x=59,8-13,7\\ x=46,1\)

B

\(\dfrac{4}{9}-\left(x-\dfrac{1}{2}\right)^2=\dfrac{1}{3}\\ \left(x-\dfrac{1}{2}\right)^2=\dfrac{4}{9}-\dfrac{1}{3}\\\left(x-\dfrac{1}{2}\right)^2=\dfrac{1}{9}\\ \left(x-\dfrac{1}{2}\right)^2=\left(\dfrac{1}{3}\right)^2\\ \Rightarrow\left[{}\begin{matrix}x-\dfrac{1}{2}=\dfrac{1}{3}\\x-\dfrac{1}{2}=-\dfrac{1}{3}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\dfrac{5}{6}\\x=\dfrac{1}{6}\end{matrix}\right. \)

`3x^{2}-7-4x=0`

`<=> 3x^{2}-4x-7=0`

`<=>3x^{2}+3x-7x-7=0`

`<=>(3x^{2}+3x)-(7x+7)=0`

`<=>3x(x+1)-7(x+1)=0`

`<=> (x+1)(3x-7)=0`

`<=>`$\left[\begin{matrix} x+1=0\\ 3x-7=0\end{matrix}\right.$

`<=>` \(\left[{}\begin{matrix}x=-1\\x=\dfrac{7}{3}\end{matrix}\right.\)

vậy `S={-1;(7)/(3)}`

b) \(xy-2x-2y=0\\ xy=0\Rightarrow x=0;y=0\\ 2x=0\\ \Rightarrow x=0\\ 2y=0\\ \Rightarrow y=0\)

\(1)3x^2-2x=0\\ \Leftrightarrow x\left(3x-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\3x-2=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{2}{3}\end{matrix}\right.\)

\(2)2x^2-10=0\\ \Leftrightarrow2x^2=10\\ \Leftrightarrow x^2=5\\ \Leftrightarrow\left[{}\begin{matrix}x=-\sqrt{5}\\x=\sqrt{5}\end{matrix}\right.\)

\(3)x^2-49=0\\ \Leftrightarrow x^2=49\\ \Leftrightarrow\left[{}\begin{matrix}x=7\\x=-7\end{matrix}\right.\)

\(4)x^2-7x+6=0\\ \Leftrightarrow x^2-x-6x+6=0\\ \Leftrightarrow x\left(x-1\right)-6\left(x-1\right)=0\\ \Leftrightarrow\left(x-1\right)\left(x-6\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-1=0\\x-6=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=1\\x=6\end{matrix}\right.\)