a: \(\left\{{}\begin{matrix}3x-7y=-14\\5x+2y=45\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}6x-14y=-28\\35x+14y=315\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}6x-14y+35x+14y=-28+315\\3x-7y=-14\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}41x=287\\7y=3x+14\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=7\\y=\dfrac{3x+14}{7}=\dfrac{3\cdot7+14}{7}=3+2=5\end{matrix}\right.\)
b: \(\left\{{}\begin{matrix}x-0,5y=-3\\2x-y=6\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}2x-y=-6\\2x-y=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x-y-2x+y=-6-6\\2x-y=6\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}0x=-12\\2x-y=6\end{matrix}\right.\Leftrightarrow\left(x;y\right)\in\varnothing\)
c: \(\left\{{}\begin{matrix}2x+3y=3\\\dfrac{2}{3}x+y=1\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}2x+3y=3\\2x+3y=3\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}2x+3y-2x-3y=3-3\\\dfrac{2}{3}x+y=1\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}0x=0\\y=1-\dfrac{2}{3}x\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\in R\\y=1-\dfrac{2}{3}x\end{matrix}\right.\)
