问题
选择题
若
|
答案
∵
=c
+2a
=(x+1,4),b
=2d
-a
=(2x-b
,3),1 2
∥c
.d
∴3(x+1)=4(2-
),1 2
解得x=1,
∴
c=(2,4),c
=(d
,3),3 2
∴
-2c
=(-1,-2),d
故选D.
若
|
∵
=c
+2a
=(x+1,4),b
=2d
-a
=(2x-b
,3),1 2
∥c
.d
∴3(x+1)=4(2-
),1 2
解得x=1,
∴
c=(2,4),c
=(d
,3),3 2
∴
-2c
=(-1,-2),d
故选D.