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已知平面直角坐标系中,点O为原点,A(-3,-4),B(5,-12),若OC=OA+OB,OD=OA-OB.(Ⅰ)求点C和点D的坐标;(Ⅱ)求OC•OD.
题目内容:
已知平面直角坐标系中,点O为原点,A(-3,-4),B(5,-12),若OC
=OA
+OB
,OD
=OA
-OB
.
(Ⅰ)求点C和点D的坐标;
(Ⅱ)求OC
•OD
.优质解答
(Ⅰ)∵OA
=(-3,-4),OB
=(5,-12),
∴OC
=OA
+OB
=(-3+5,-4-12)=(2,-16),
OD
=OA
-OB
=(-3-5,-4+12)=(-8,8);
∴点C(2,-16),点D(-8,8);
(Ⅱ)OC
•OD
=2×(-8)+(-16)×8=-144.
OC |
OA |
OB |
OD |
OA |
OB |
(Ⅰ)求点C和点D的坐标;
(Ⅱ)求
OC |
OD |
优质解答
OA |
OB |
∴
OC |
OA |
OB |
OD |
OA |
OB |
∴点C(2,-16),点D(-8,8);
(Ⅱ)
OC |
OD |
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