5x+3y=4a
10x+6y=8a
10x+6y-3=8a-3=4x-5y
即有6x+11y=3①
5x+3y=4a
6x-2y=9a
消去a有 3x+5y=0②
①②联立解得
x=-5,y=3
带入式子5x+3y=4a中,解得a=-4
x= -5,y=3,a= -4