pp-T1-DS148

[Huang Hsin-Yi]

148.
In the xy-plane, does the line with equation y = 3x + 2 contain the point (r, s) ?

(1) (3r + 2 - s)(4r + 9 - s) = 0

(2) (4r - 6 - s)(3r + 2 - s) = 0

ANS:C

[puja]

148.
In the xy-plane, does the line with equation y = 3x + 2 contain the point (r, s) ?

(1) (3r + 2 - s)(4r + 9 - s) = 0

(2) (4r - 6 - s)(3r + 2 - s) = 0

ANS:C

我的理解是:
若(r,s)為 y=3x+2上的一點,則 (r, 3r+2)----->s=3r+2

1)(3r + 2 - s)=0 或 (4r + 9 - s) = 0
s=3r+2 或 s=4r+9 不充分
2) (4r - 6 - s)=0或(3r + 2 - s)=0 不充分,同上

1)-2) 則 15(3r + 2 - s)=0----->s=3r+2 充分

[Huang Hsin-Yi]

感謝
原來我沒算到最後