`a)x-2y=3<=>y=1/2x-3/2` `(d')`
Để `(d) \bot (d')<=>a.a'=-1`
`<=>(m-2). 1/2=-1`
`<=>m=0`
Vậy `m=0;n in RR` thì `(d)\bot(d')`
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`b)3x+2y=1<=>y=-3/2x+1/2` `(\Delta)`
Để `(d) //// (\Delta)<=>{(a=a'),(b \ne b'):}`
`<=>{(m-2=-3/2<=>m=1/2),(n \ne 1/2):}`
Vậy `m=1/2;n \ne 1/2`
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`c)y-2x+3=0<=>y=2x-3` `(\Delta')`
Để `(d)` trùng `(\Delta')<=>{(a=a'),(b=b'):}`
`<=>{(m-2=2<=>m=4),(n=3):}`
Vậy `m=4;n=3` thì `(d)` trùng `(\Delta')`