Giai hệ PT bằng phương pháp cộng
a.\(\left\{{}\begin{matrix}5.\left(x+2y\right)-3.\left(x-y\right)=99\\x-3y=7x-4y-17\end{matrix}\right.\)
b.\(\left\{{}\begin{matrix}3.\left(y-5\right)+2\left(x-3\right)=0\\7.\left(x-4\right)+3\left(x+y-1\right)=14\end{matrix}\right.\)
c.\(\left\{{}\begin{matrix}2.\left(x+1\right)-5\left(y+1\right)=8\\3.\left(x+1\right)-2.\left(y+1\right)=1\end{matrix}\right.\)
d.\(\left\{{}\begin{matrix}2.\left(3y+1\right)-4\left(x-1\right)=5\\5.\left(3y+1\right)-8\left(x-1\right)=9\end{matrix}\right.\)
d: =>6y+2-4x+4=5 và 15y+5-8x+8=9
=>-4x+6y=-1 và -8x+15y=-4
=>x=-3/4; y=-2/3
c: \(\Leftrightarrow\left\{{}\begin{matrix}x+1=-1\\y+1=-2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-2\\y=-3\end{matrix}\right.\)
b: \(\Leftrightarrow\left\{{}\begin{matrix}3y-15+2x-6=0\\7x-28+3y+3y-3=14\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x+3y=21\\7x+6y=45\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=\dfrac{19}{3}\end{matrix}\right.\)