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9.已知過點A(-2,m)和B(m,4)的直線與直線2x+y-1=0平行,則m的值為(B)
(A)0 (B)-8 (C)2 (D)10
10從原點向圓 x2+y2-12y+27=0作兩條切線,則該圓夾在兩條切線間的劣弧長為(B )
(A)π (B)2π (C)4π (D)6π
11若直線按向量平移后與圓相切,則c的值為( A )
A.8或-2 B.6或-4 C.4或-6 D.2或-8