题目

若直线2x-y+λ=0按向量a=(1,-1)平移后与圆x2+y2+2x+4y=0相切,则实数λ的值为A.8或-2              B.6或-4               C.4或-6                D.2或-8 答案：A解析:直线2x-y+λ=0按向量a=(1,-1)平移后,得2x-y+λ-3=0,圆x2+y2+2x+4y=0配方,得(x+1)2+(y+2)2=5.若直线与圆相切,则=,解得λ=-2或λ=8.

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