lee8283
幼苗
共回答了18个问题采纳率:88.9% 举报
① 3x+y=5,---------(1)
5x+3y=19; ----------(2)
(1)*3-(2)得
4x=-4,x=-1,y=8
② x/2+y/3=7, 3x+2y=42---------(1)
3(x-2)=2(y-9);3x-2y=-12--------(2)
(1)+(2)式得
6x=30,x=5,y=27/2
③ 5a-3b=-6,----------(1)
4a-1=3b;4a-3b=1-------(2)
(1)-(2)式得
a=-7,b=-29/3
④ 2x-3y-8=0, ---------(1)
7x-5y+5=0;-------------(2)
(1)*5-(2)*3得
-11x-55=0
x=-5,y=-6
⑤ 2x+y=7,----------(1)
x+2y=8;-------------(2)
(1)*2-(2)式得
3x=6,x=2,y=3
⑥ x+y=4,-----------(1)
80%x+15%y=20%×4,0.8x+0.15y=0.8---------(2)
(1)*0.8-(2)式得
0.65y=2.4
y=2.4/0.65=48/13
x=4/13
1年前
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