Urgent questions(2) ^_^

x - y = 6

y = x - 6 and x = y + 6

So,

3x + ( x - 6 ) > 6

3x + x > 12

x > 3

3 ( y + 6 ) + y > 6

3y + 18 + y > 6

4y > - 12

y > - 3


2007-08-07 00:33:05 補充：
To solve this question, mark x and y as the subject in x - y = 6 respectively and then put them back into 3x + y > 6. You will get the answer after solving the inequalities.

3x + y >6...(1) and
x - y = 6...(2)

From (2),
x = 6 + y ...(3) and
y = x - 6 ...(4)

Put (3) into (1),
3( 6 + y) > 6
18 + 3y > 6
3y > 6 - 18
3y > -12
y > -4

Put (4) into (1),
3x + ( x - 6 ) > 6
4x - 6 > 6
4x > 12
x > 3

2007-08-07 01:19:11 補充：
sorry@@... there is something wrong...in part 3, it should be like this:Put (3) into (1),３（６＋ｙ）＋ｙ＞６１８＋３ｙ＋ｙ＞６４ｙ＞６－１８４ｙ＞－１２ｙ＞－３ｓｏ　ｔｈｅ　ａｎｓｗｅｒ　ｓｈｏｕｌｄ　ｂｅ：ｘ＞３　，　ｙ＞－３

3x+y>6...(1)
x-y=6...(2)
From(2), we have
x=y+6
Put it into (1)
3(y+6)+y>6
4y>-12
y>-3
x-6>-3
x>3

x>3, y>-3