3X-Y=7 一亞亞亞一亞一亞亞一一

1. 1) 3X-Y=7
2) 3X+2Y=13

2)-1), 3X + 2Y-(3X -Y)=13-7
3Y = 6
Y=2
sub. Y=2 into 1), 3X-2=7
3X=9
X=3

X=3, Y=2

2. 因問題不清楚, 5除3剩Y.= 5/(3Y) 定 (5/3)*Y ? 現做(5/3)*Y.

1) 7X+3Y+2=0
2) (5/3)Y=X-6

from 2), 5Y = 3X - 18
3X - 5Y - 18 =0 (3)

1)*3 - (3)*7, 21X + 9Y + 6 - 21X + 35Y + 126 = 0
44Y + 132 = 0
44Y = -132
Y = -3

sub y = -3 into 1), 7X + 3(-3) + 2 = 0
7X -7 = 0
7X = 7
X = 1

X=1, Y=-3

一. 3x-y=7........ (1)
3x+2y=13......(2)
(2)-(1)得3y=6
y=2
將 y=2帶入(1)得3x-2=7
3x=9
x=3
所以xy=6

二. 7x+3y+2=0......(1)
5y除3= x-6......(2)
由(2)*3得 5y=3x-18......(3)
(1)*3-(3) *7得 21x-21x+9y+35y+6+1262=0
44y= -132
y= -3
將 y= -3帶入(1)得 7x-9+2=0
x=1
所以xy= -2