题目内容

(本小题满分14分)已知直线。问为何值时,有:(1)?(2)
解:由,得;   ·········3分
当m=4时,l1:6x+7y-5=0,l2:6x+7y=5,即l1与l2重合;
时,即l1∥l2.
∴当时,l1∥l2. ·        ········································7分
(2)由
∴当m=-1或m=-时,l1⊥ l2. · ·······································14分
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