Question

2.用代入消元法解下列方程组

Answer 1

⑴:由①得:x=3+y,代入②得:5(3+y)+2y=4.解得y=-11/7.把y=-11/7代入x=3+y得:x=3-11/7=10/7.所以x=10/7.y=-11/7.
⑵:由②得:x=3-4y,代入①得:3(3-4y)-2y=9.解得y=0.把y=0代入x=3-4y得:x=3.所以x=3.y=0.
⑶:由②得:x=3-2y,代入①得:3-2y-(y-5)/2=0.解得y=11/5.把y=11/5代入x=3-2y得:x=3-2(11/5)=-7/5.所以x=-7/5.y=11/5.
⑴:由①得:x=2+y/2,代入②得:2(2+y/2)+3y=3.解得y=-1/4.把y=-1/4代入x=2+y/2得:x=2-(1/4)/2=15/8.所以x=15/8.y=-1/4.

Answer 2

（4）由X=2+2分子Y,代入二式就可解答